[Bug]: Odd config file requirements to get "complex" cosmosdb_nosql to work

### What happened?

I have the following `cosmosdb_nosql` data setup with a database and 2 containers, `conferences` and `talks`:

data setup

- **database**
- conferences
- ```json
[
{
"endDate": "2022-06-01",
"id": "072d1638-a763-49f7-850f-763eed777837",
"location": "",
"mainTag": "",
"name": "CONFERENCE",
"startDate": "2022-06-01",
"url": "https://example.com/",
"year": 2022,
"talks": [
{
"abstract": "EXAMPLE",
"mainTag": "",
"tags": [],
"talkId": "0c8c7101-26ee-42e9-9596-32ec1d229c0b",
"talkLength": 50,
"talkTime": null,
"title": "EXAMPLE"
}
]
}
]
- talks
- ```json
[
{
"id": "f45a36c0-4031-4779-9461-eeedf37a7b74",
"mainTag": "Software Development",
"title": "EXAMPLE"
}
]
```

The important thing to notice is that there are **3** models, of which **2** need to be exposed as their own entities in DAB:
- Conference (**Exposable**)
- Talk (**Exposable**)
- ConferenceTalk
- Part of `Conference`, but not its own entity that needs to be exposed!

I [read the docs](https://learn.microsoft.com/en-us/azure/data-api-builder/quickstart-nosql#create-configuration-files) which tell me I need to define a graphql schema, on top of the `dab-config.json`, which I imagine has to look like this:

GraphQL schema

```graphql
type Conference @model {
id: ID!
name: String!
location: String
year: Int!
startDate: String
endDate: String
url: String
mainTag: String
talks: [ConferenceTalk!]!
}

type ConferenceTalk {
talkId: ID!
title: String!
abstract: String
mainTag: String
talkTime: String
talkLength: Int
tags: [String]
}

type Talk @model {
id: ID!
title: String!
mainTag: String
}
```

Which leads me to my `dab-config.json`, which looks like this.

dab-config.json

```json
{
"$schema": "https://github.com/Azure/data-api-builder/releases/download/v1.2.10/dab.draft.schema.json",
"data-source": {
"database-type": "cosmosdb_nosql",
"connection-string": "@env('COSMOSDB_CONNECTIONSTRING')",
"options": {
"database": "database",
"container": null,
"schema": "schema.gql"
}
},
"runtime": {
"rest": {
"enabled": false,
"path": "/api",
"request-body-strict": true
},
"graphql": {
"enabled": true,
"path": "/graphql",
"allow-introspection": true
},
"host": {
"cors": {
"origins": [],
"allow-credentials": false
},
"authentication": {
"provider": "StaticWebApps"
},
"mode": "development"
}
},
"entities": {
"Conference": {
"source": {
"object": "conferences"
},
"graphql": {
"enabled": true,
"type": {
"singular": "Conference",
"plural": "Conferences"
}
},
"rest": {
"enabled": false
},
"permissions": [
{
"role": "anonymous",
"actions": [
{
"action": "read"
}
]
}
]
},
"Talk": {
"source": {
"object": "talks"
},
"graphql": {
"enabled": true,
"type": {
"singular": "Talk",
"plural": "Talks"
}
},
"rest": {
"enabled": false
},
"permissions": [
{
"role": "anonymous",
"actions": [
{
"action": "read"
}
]
}
]
},
"ConferenceTalk": {
"source": {
"object": "WE_DO_NOT_EXPOSE_THIS_BUT_NEED_IT_TO_GET_DAB_TO_WORK"
},
"graphql": {
"enabled": false
},
"rest": {
"enabled": false
},
"permissions": [
{
"role": "anonymous",
"actions": [
{
"action": "read"
}
]
}
]
}
}
}
```

# The problem
I struggled with this for a **long** while. In order to get both `ConferenceTalk` and `Talk` to work, I must define `ConferenceTalk` as an entity in `dab-config.json`, which is what the error also says. However, this doesn't make sense because `ConferenceTalk` is not its own entity and should not need to be exposed.

# Expected solution
I should not need to define entities like `ConferenceTalk` in `dab-config.json` for objects that are part of main/parent entities. What if I had objects 10 layers deep? Would I need to define all of them as entities in `dab-config.json`? This would lead to a huge `dab-config.json` with filler data, just like `ConferenceTalk` is now.

## Extra
Please improve the docs about defining graphql yourself for cosmosdb. They're very limited. I have no idea why/if I need to define `@model`, for example.

### Version

Microsoft.DataApiBuilder 1.2.10+c7ca8db8558a63919c530e454c8f18b45d5b931c

### What database are you using?

CosmosDB NoSQL

### What hosting model are you using?

Local (including CLI)

### Which API approach are you accessing DAB through?

GraphQL

### Relevant log output

```Text
Azure.DataApiBuilder.Service.Startup[0]
Unable to complete runtime initialization. Refer to exception for error details.
Azure.DataApiBuilder.Service.Exceptions.DataApiBuilderException: The entity 'ConferenceTalk' was not found in the runtime config.
at Azure.DataApiBuilder.Core.Services.MetadataProviders.CosmosSqlMetadataProvider.AssertIfEntityIsAvailableInConfig(String entityName) in /_/src/Core/Services/MetadataProviders/CosmosSqlMetadataProvider.cs:line 296
at Azure.DataApiBuilder.Core.Services.MetadataProviders.CosmosSqlMetadataProvider.ProcessSchema(IReadOnlyList`1 fields, Dictionary`2 schemaDocument, String currentPath, IncrementingInteger tableCounter, EntityDbPolicyCosmosModel parentEntity, HashSet`1 visitedEntities) in /_/src/Core/Services/MetadataProviders/CosmosSqlMetadataProvider.cs:line 228
at Azure.DataApiBuilder.Core.Services.MetadataProviders.CosmosSqlMetadataProvider.ParseSchemaGraphQLFieldsForJoins() in /_/src/Core/Services/MetadataProviders/CosmosSqlMetadataProvider.cs:line 180
at Azure.DataApiBuilder.Core.Services.MetadataProviders.CosmosSqlMetadataProvider..ctor(RuntimeConfigProvider runtimeConfigProvider, IFileSystem fileSystem) in /_/src/Core/Services/MetadataProviders/CosmosSqlMetadataProvider.cs:line 85
at Azure.DataApiBuilder.Core.Services.MetadataProviders.MetadataProviderFactory..ctor(RuntimeConfigProvider runtimeConfigProvider, IAbstractQueryManagerFactory queryManagerFactory, ILogger`1 logger, IFileSystem fileSystem, Boolean isValidateOnly) in /_/src/Core/Services/MetadataProviders/MetadataProviderFactory.cs:line 32
at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
at System.Reflection.MethodBaseInvoker.InvokeWithManyArgs(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, RuntimeResolverContext context)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitRootCache(ServiceCallSite callSite, RuntimeResolverContext context)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.CreateServiceAccessor(ServiceIdentifier serviceIdentifier)
at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(ServiceIdentifier serviceIdentifier, ServiceProviderEngineScope serviceProviderEngineScope)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type serviceType)
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider)
at Azure.DataApiBuilder.Service.Startup.PerformOnConfigChangeAsync(IApplicationBuilder app) in /_/src/Service/Startup.cs:line 620
fail: Azure.DataApiBuilder.Service.Startup[0]
Could not initialize the engine with the runtime config file: dab-config.json
info: Microsoft.Hosting.Lifetime[0]
Application is shutting down...
fail: Microsoft.Extensions.Hosting.Internal.Host[11]
Hosting failed to start
System.Threading.Tasks.TaskCanceledException: A task was canceled.
at Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServerImpl.BindAsync(CancellationToken cancellationToken)
at Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServerImpl.StartAsync[TContext](IHttpApplication`1 application, CancellationToken cancellationToken)
at Microsoft.AspNetCore.Hosting.GenericWebHostService.StartAsync(CancellationToken cancellationToken)
at Microsoft.Extensions.Hosting.Internal.Host.b__15_1(IHostedService service, CancellationToken token)
at Microsoft.Extensions.Hosting.Internal.Host.ForeachService[T](IEnumerable`1 services, CancellationToken token, Boolean concurrent, Boolean abortOnFirstException, List`1 exceptions, Func`3 operation)
Unable to launch the Data API builder engine.
Error: Failed to start the engine.
```

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