search_term in List Room Admin API is case sensitive

[aaronraimist]

It probably should be case insensitive

https://github.com/matrix-org/synapse/blob/develop/docs/admin_api/rooms.md#list-room-api

[dklimpel]

The same problem for name in user list
https://github.com/matrix-org/synapse/blob/develop/docs/admin_api/user_admin_api.rst#list-accounts

Related: #6268

[MurzNN]

Maybe the source of this problem is same like in #3116 with room events search?