func init --docker-only should support .NET Solutions

## Issue

When running

```sh
func init --docker-only --worker-runtime dotnet
```
against a csproj I get a dockerfile that only includes the current directory

## Outcome

```sh
docker build -t repo/image:tag .
```

Fails due to not being able to find dependent projects

## Impact

I can't generate dockerfiles as part of my CI / CD pipeline, which could be argued is a bad thing, but I like the idea of a function being "take my code and run it" and as long as the function runtime is there I don't care if it is running locally, in Azure Function or in KEDA.

## Expected outcome

When running

```sh
func init --docker-only --worker-runtime dotnet
```

It should include dependent projects into the dockerfile using "COPY" this will then allow for dependent projects to be included and also match the "Add docker support" at a project level in Visual Studio.

Start at the `func init --docker-only --worker-runtime dotnet` entry point and inspect how Dockerfiles are generated for a `.csproj`. Trace how dependent projects are identified, then verify that the generated Dockerfile includes them with `COPY` entries and that `docker build -t repo/image:tag .` can find those dependencies.

Written by the indexing model from the issue text.