[TECH DEBT] Deprecate Zabbix Modules

[garethgreenaway]

Description of the tech debt to be addressed, include links and screenshots

Deprecating all Zabbix functionality in Salt and moving it to:
https://github.com/salt-extensions/saltext-zabbix

First Salt version with Vault no longer present in the core: 3009.0

To be removed:

tests/pytests/unit/modules/test_zabbix.py
tests/pytests/unit/states/zabbix
salt/modules/zabbix.py
salt/returners/zabbix_return.py
salt/states/zabbix_usergroup.py
salt/states/zabbix_user.py
salt/states/zabbix_template.py
salt/states/zabbix_usermacro.py
salt/states/zabbix_valuemap.py
salt/states/zabbix_action.py
salt/states/zabbix_mediatype.py
salt/states/zabbix_host.py
salt/states/zabbix_hostgroup.py
doc/ref/modules/all/salt.modules.zabbix.rst
doc/ref/returners/all/salt.returners.zabbix_return.rst
doc/ref/states/all/salt.states.zabbix_action.rst
doc/ref/states/all/salt.states.zabbix_valuemap.rst
doc/ref/states/all/salt.states.zabbix_host.rst
doc/ref/states/all/salt.states.zabbix_usermacro.rst
doc/ref/states/all/salt.states.zabbix_template.rst
doc/ref/states/all/salt.states.zabbix_hostgroup.rst
doc/ref/states/all/salt.states.zabbix_user.rst
doc/ref/states/all/salt.states.zabbix_mediatype.rst
doc/ref/states/all/salt.states.zabbix_usergroup.rst

[OrangeDog]

It's not a cloud thing...