Implement getBulkSecret API

[mukundansundar]

Describe the proposal

Following the implementation in runtime, dapr/dapr#2168, implement the getBulkSecret for both HTTP and gRPC.
Implement unit tests.
Implement integration tests for both HTTP and gRPC APIs.
Modify secrets example for this API and add javadoc for the API.

[arghya88]

/assign

[mukundansundar]

Hi @arghya88, thanks for picking this up. Are you working on this?

[arghya88]

@mukundansundar yes started on it. Will have a PR soon.

[artursouza]

@arghya88 Any updates on this issue?

[artursouza]

I have a PR for this. See above.