Adds functionality to control the room creation and retrieval responses
using the `X-Fields` and `X-Expand` headers.
- `X-Fields` allows clients to specify which fields to include in the
response, optimizing bandwidth usage.
- `X-Expand` allows clients to request the full data of expandable
properties, such as `config`, avoiding subsequent GET requests.
This change introduces new request validators, service methods, and
helper functions to handle the header logic and process the room objects accordingly.
d4a87f8a45