Instead of using internal functions for data setup,
we use the API so that these tests are more
end-to-end.
This commit also removes a now unnecessary
`if date_muted is None` check.
This cleans up some code added in 3bfcaa3968.
Also fixes some indentation to be more readable:
- `mock.patch` is in a single line.
- Dictionaries are one field per line.
Adds backend code for the mute users feature.
This is just infrastructure work (database
interactions, helpers, tests, events, API docs
etc) and does not involve any behavioral/semantic
aspects of muted users.
Adds POST and DELETE endpoints, to keep the
URL scheme mostly consistent in terms of `users/me`.
TODOs:
1. Add tests for exporting `zulip_muteduser` database table.
2. Add dedicated methods to python-zulip-api to be used
in place of the current `client.call_endpoint` implementation.