Add OAuth2 to the Helidon gRPC endpoints.

[jsync-swirlds]

Add an OAuth2 requirement to all of the current API endpoints for Block Node. This should include configuring the Helidon layer to redirect to our custom OAuth2 authentication server and validating the OAuth2 token provided with each authenticated request.

This does not include any work on the custom authentication server, and fully trusts the authentication server (i.e. if the OAuth2 token is valid, we accept its assertions as-is).