/directory/room{roomAlias} leaks all involved homeservers

**Link to problem area**:

https://spec.matrix.org/v1.11/client-server-api/#get_matrixclientv3directoryroomroomalias

**Issue**
What is wrong? How can we improve?

The spec for resolving [room aliases to IDs](https://spec.matrix.org/v1.11/client-server-api/#get_matrixclientv3directoryroomroomalias) doesn't specify any limits on the returned `servers` list resulting in strange occurences like ~400 servers (grew significantly since I raised the [synapse issue](https://github.com/element-hq/synapse/issues/17298)) on `#jellyfinorg:matrix.org` for example.

I believe this is wasteful and a privacy concern and that the list should be perhaps artifically capped and maybe ordered by the _size_ of the homeserver (number of active users?).

Start with the GET /_matrix/client/v3/directory/room/{roomAlias} section in the linked Matrix Client-Server API specification and review the linked Synapse issue for the observed server-list behavior. Clarify the desired limit and ordering rules with the existing discussion; done means the specification records an agreed change that addresses the excessive disclosure and response size.

Written by the indexing model from the issue text.