API - Allow specifying tiering information in bucket.create_bucket call.

[nb-ohad]

Current behavior

In order to create a bucket using the rpc api we need to first create a tier then a tiering policy then the bucket (in that order) from the client.

Recommended behavior

Allow specifying tiring information as a parameter for create_bucket which will create the desired entities in the backend which can e done in one make_changes call.