Allow Synapse Admin API's Room Search to accept non-ASCII characters (#10859)

* add tests for checking if room search works with non-ascii char

* change encoding on parse_string to UTF-8

* lints

* properly encode search term

* lints

* add changelog file

* update changelog number

* set changelog entry filetype to .bugfix

* Revert "set changelog entry filetype to .bugfix"

This reverts commit be8e5a314251438ec4ec7dbc59ba32162c93e550.

* update changelog message and file type

* change parse_string default encoding back to ascii and update room search admin api calll to parse string

* refactor tests

* Update tests/rest/admin/test_room.py

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>