Initial support of dynamic auth providers for MCP

[TylerLeonhardt]

With this change, we support being able to on-the-fly create an Auth Provider based on an oauth-authorization-server's metadata.

MCP then leverages this because by following the MCP spec we can figure out the oauth server metadata and then request a token from that server.

The tokens are persisted and will be refreshed on demand... all based on the OAuth spec.

Fixes https://github.com/microsoft/vscode/issues/247759