🥕[Bug]: `dab validate` blows up on invalid JSON.

Remove "permissions" from one of the entities in an otherwise valid configuration file.

> Or just misspell "permissions", same result.

Then run `dab validate`

```
C:\Temp\dab\Working>dotnet dab validate
Information: Microsoft.DataApiBuilder 1.3.19
Information: Config not provided. Trying to get default config based on DAB_ENVIRONMENT...
Information: Environment variable DAB_ENVIRONMENT is (null)
Information: Validating config file: dab-config.json
Loading config file from C:\Temp\dab\dotnet-template\Api\Working\dab-config.json.
Unhandled exception. System.AggregateException: One or more errors occurred. (Object reference not set to an instance of an object.)
---> System.NullReferenceException: Object reference not set to an instance of an object.
at Azure.DataApiBuilder.Core.Configurations.RuntimeConfigValidator.ValidatePermissionsInConfig(RuntimeConfig runtimeConfig) in /_/src/Core/Configurations/RuntimeConfigValidator.cs:line 733
at Azure.DataApiBuilder.Core.Configurations.RuntimeConfigValidator.TryValidateConfig(String configFilePath, ILoggerFactory loggerFactory) in /_/src/Core/Configurations/RuntimeConfigValidator.cs:line 154
--- End of inner exception stack trace ---
at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
at Cli.ConfigGenerator.IsConfigValid(ValidateOptions options, FileSystemRuntimeConfigLoader loader, IFileSystem fileSystem) in /_/src/Cli/ConfigGenerator.cs:line 1709
at Cli.Commands.ValidateOptions.Handler(ILogger logger, FileSystemRuntimeConfigLoader loader, IFileSystem fileSystem) in /_/src/Cli/Commands/ValidateOptions.cs:line 31
at Cli.Program.<>c__DisplayClass2_0.b__5(ValidateOptions options) in /_/src/Cli/Program.cs:line 67
at CommandLine.ParserResultExtensions.MapResult[T1,T2,T3,T4,T5,T6,T7,T8,TResult](ParserResult`1 result, Func`2 parsedFunc1, Func`2 parsedFunc2, Func`2 parsedFunc3, Func`2 parsedFunc4, Func`2 parsedFunc5, Func`2 parsedFunc6, Func`2 parsedFunc7, Func`2 parsedFunc8, Func`2 notParsedFunc)
at Cli.Program.Execute(String[] args, ILogger cliLogger, IFileSystem fileSystem, FileSystemRuntimeConfigLoader loader) in /_/src/Cli/Program.cs:line 61
at Cli.Program.Main(String[] args) in /_/src/Cli/Program.cs:line 41
```

Of all CLI methods, `validate` should handle exceptions with elegance.

## Solution

"Config file is not valid" at a minimum.

"`permissions` property is required on entity `Actor`" would be ideal.

Beginnen Sie in src/Core/Configurations/RuntimeConfigValidator.cs bei ValidatePermissionsInConfig, Zeile 733, und folgen Sie dann TryValidateConfig sowie den Einstiegspunkten des validate-Befehls in src/Cli/ConfigGenerator.cs und src/Cli/Commands/ValidateOptions.cs. Reproduzieren Sie das Problem mit einer ansonsten gültigen Konfiguration, in der permissions fehlt oder falsch geschrieben ist. Erledigt ist es, wenn dab validate eine ungültige Konfiguration meldet, statt mit einer unbehandelten NullReferenceException zu terminieren, und idealerweise die fehlende Property und Entität angibt.

Vom Indexierungsmodell aus dem Issue-Text verfasst.