Intent of TestExtractMetadataFromTrailer_EmptyProtoMetadata

All 4 exact tests in this concept. Every test is marked by where it enters the hierarchy.

go.temporal.io/ 4 tests
- server/ 4 tests
  - common/ 4 tests
    
    rpc/ 4 tests
    
    interceptor/ 4 tests
    
    go.temporal.io/server/common/rpc/interceptor/TestExtractMetadataFromTrailer_ControlCharsInProto Inherited TestExtractMetadataFromTrailer_PrefersProtoKey, TestExtractMetadataFromTrailer_ControlCharsInProto
    
    go.temporal.io/server/common/rpc/interceptor/TestExtractMetadataFromTrailer_EmptyProtoMetadata Introduced here
    
    go.temporal.io/server/common/rpc/interceptor/TestExtractMetadataFromTrailer_PrefersProtoKey Inherited TestExtractMetadataFromTrailer_PrefersProtoKey, TestExtractMetadataFromTrailer_ControlCharsInProto
    
    go.temporal.io/server/common/rpc/interceptor/TestExtractMetadataFromTrailer_ProtoRoundTrip Inherited TestExtractMetadataFromTrailer_ProtoRoundTrip