Change Zabbix alerter

[timeforplanb123]

Description

Add the ability to specify zbx_host from available elasticsearch field.

By default, zabbix alerter send "1" to single host with specified zbx_host hostname. For a large number of hosts in zabbix, it would be convenient to specify zbx_host value from available elasticsearch field.

More details - #812

Checklist

• I have reviewed the contributing guidelines.
• I have included unit tests for my changes or additions.
• I have successfully run make test-docker with my changes.
• I have manually tested all relevant modes of the change in this PR.
• I have updated the documentation.
• I have updated the changelog.

Questions or Comments

[nsano-rururu]

Add the following verification check settings.
https://github.com/jertel/elastalert2/blob/master/elastalert/schema.yaml#L688

zbx_host_from_field: {type: boolean}

[timeforplanb123]

Added

[jertel]

@nsano-rururu are you ok with the style changes being made with this commit? We usually ask that contributors adopt the existing style already used within the source code, to avoid having a mixture of varying coding styles within the project. If that's not important to you we can accept it as-is.

Ex:

[nsano-rururu]

If you want to modify existing code, it's best to follow your existing coding style.

[timeforplanb123]

So I need to change the black formatted code and return to the current style?

[jertel]

That screenshot I pasted was a small example. What we would prefer is to undo all of your formatting changes, and only submit the logic changes required for your PR functionality.

[timeforplanb123]

Fixed :)

[jertel]

Thanks for the contribution!