Investigate lifetime issues for `*project.ProjectConfig`

[ellismg]

We currently register *project.ProjectConfig as a Singleton because we want a single version that is shared across the system to allow things like hooks to work.

This leads to some problems where if azure.yaml doesn't exist yet - we end up storing a nil value in the container - even if it could resolve later, which breaks some vs-server flows.

For preview 3 we have the vs-server register it as transient - which is what the VS Team tested and signed off on. This work item resolves fixing this "the right way" and discovering what "the right way" means.

It seems like the current registrations for Lazy[*project.ProjectConfig] and *project.ProjectConfig are also broken in subtle ways. The implementation of the Lazy version in terms of the prompt one may be wrong.

[weikanglim]

With #3381 we move slightly backwards to make server-handling mimic the CLI paradigm; thus, a singleton project config would have lifetime to be request-scoped. I removed the TODO as a result.

This may still be fair game:

The implementation of the Lazy version in terms of the prompt one may be wrong.