Added tests for streaming calls

[ST-DDT]

Features

• Added AnonymousAuthenticationReader to allow some calls to skip authentication, when using AuthorizationCheckingServerInterceptor.
• Added some convenience methods to AccessPredicate
• Added tests for streaming calls
• Fixed missing AccessDeniedException -> AuthenticationException transformations

TBD

• I noticed that the permitAll access setting does not allow unauthenticated users to access the methods, if anonymous authentication is not enabled. Should I add/change it to an explicit permitAll?

[yidongnan]

I think you can add/change it to an explicit permitAll or explain it clearly in the readme, otherwise some issues may appear.

[ST-DDT]

I checked the current spring-provided structure and AFAICT it is not possible to add an explicit "permitAll". Thus, I changed the logic a bit to use null as public access. However, I'm not sure whether null is a good value to disable security. As an alternative I thought about adding a setPublic(MethodDescriptor) method to ManualGrpcSecurityMetadataSource. What do you think?

[ST-DDT]

I guess I'll use a constant for now.

[yidongnan]

LGTM. I think the way to use constants is acceptable.