Moira-python-client

Add support for multiple clusters in trigger creation

Now you can use `cluster_id` field in api to set non-default cluster for remote triggers. List of available clusters can be seen in api at `https://your-moira-url/api/config`

Add support for prometheus trigger creation.

Now you can use `trigger_source` field in api that overrides `is_remote` field

Fix typo

Small refactor to satisfy users that use Python < 3.6

Make validation for Python-client like validation in Web Moira. It is need to make valiation right and unified for all Moira client sides.

[Use new validation for creating/updating triggers](https://github.com/moira-alert/python-moira-client/commit/3edb4c720d4b80ae8a4bd6117cb2b9cf0c5bec16)

[Return response object instead of string ID](https://github.com/moira-alert/python-moira-client/commit/5f2bccdd11d6ef6a2a548b9c7072037ebf0445c0)

‼️ Remove underscore-prefixed fields that contained scheduling time settings:

- `_start_hour`
- `_start_minute`
- `_end_hour`
- `_end_minute`
- `_timezone_offset`
- `disabled_days`

Because they were duplicates of data from sched field.

Please use sched field for scheduling settings instead.