Support passing OpenAPI spec version and document name via dotnet-getdocument

[captainsafia]

The getdocument API for resolving documents at build-time only supports serializing documents to the spec version serialized via OpenAPI options. We want to add support for overriding this option for integration scenarios where 3rd-party tools might support only certain versions of the OpenAPI specification.

This PR:

• Adds a new --openapi-version flag to the getdocument CLI application to support setting the OpenAPI spec version to use when generating documents
• Adds a new --document-name flag to the getdocument CLI application to support generating the OpenAPI file for a given document
• Add a new GenerateAsync method to the IDocumentProvider interface to support passing the OpenAPI spec version during serialization
• Adds tests for the GetDocument tool

Sample invocation:

$ dotnet dotnet-getdocument.dll --assembly ~/gh/aspnetcore/artifacts/bin/Sample/Debug/net9.0/Sample.dll
	--project ./Sample.csproj --file-list ~/gh/aspnetcore/artifacts/obj/Sample/Debug/net9.0/Sample.OpenApi.cache
	--output ~/test.json --openapi-version OpenApi2_0
	--tools-directory /Users/captainsafia/gh/aspnetcore/artifacts/bin/GetDocument.Insider/Debug/net9.0/
	--framework ".NETCoreApp,Version=v9.0"
	--document-name internal

[amcasey]

--openapi-version OpenApi2_0

I'm assuming this is an enum member, but it seems a little clunky - I feel like I'd expect to pass "2.0" or something. But maybe we don't expect the tool to have any human users?

[captainsafia]

--openapi-version OpenApi2_0

I'm assuming this is an enum member, but it seems a little clunky - I feel like I'd expect to pass "2.0" or something. But maybe we don't expect the tool to have any human users?

Yep, this maps directly to the OpenApiSpecVersion enum supported by the OpenAPI package (ref). We could prettify the value expected here but I liked being able to pass it directly to Enum.TryParse without any further modification.

I don't anticipate that users will interact with these parameters and if they do it would be through MSBuild properties/Visual Studio config.

[amcasey]

I have some concerns about validation but seems generally good.

[amcasey]

Some nits about resource strings, but LGTM. Thanks for the changes!