Document usage of _FunctionsSkipCleanOutput and FunctionsPreservedDependencies

[mattchenderson]

_FunctionsSkipCleanOutput and FunctionsPreservedDependencies do not have full coverage in official documentation. These should be covered in https://learn.microsoft.com/en-us/azure/azure-functions/functions-dotnet-class-library

This is a tracking item for this repo in support of other work items here. An item has also been filed in an internal docs system as part of the standard process there.

[fowl2]

for reference, this was previously rejected here: MicrosoftDocs/azure-docs#77460

[xerootg]

I used @fowl2 's blog to resolve an assembly resolution issue that has been really difficult to figure out. Please consider getting this documented. Users of Function really need help here.

[sipkode]

This still seems to be an issue. While it would be amazing if the underlying issue could be fixed, I'd settle for this being documented at least. I found my way here through this issue: Azure/azure-functions-vs-build-sdk#397, as I hit the "Cannot load assembly" issue today when I moved some functions that rely on System.IdentityModel.Tokens.Jwt into a library.