Add shortcut to set API key

[Quinn-With-Two-Ns]

closes #1997

Add shortcut to add an api key to a connection. Instead of

    WorkflowServiceStubsOptions.Builder stubOptions =
        WorkflowServiceStubsOptions.newBuilder()
             ...
            .addGrpcMetadataProvider(
                new AuthorizationGrpcMetadataProvider(() -> "Bearer " + API_KEY))

Users can now set

    WorkflowServiceStubsOptions.Builder stubOptions =
        WorkflowServiceStubsOptions.newBuilder()
             ...
            .addApiKey(
                () -> API_KEY)

[Quinn-With-Two-Ns]

@cretz Is this what you had in mind as a shortcut?

[cretz]

Yes, this makes sense to me