add_alertmanager_resolve_timeout

[eveningcafe]

Description

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

[eveningcafe]

The thing is, alertmanager has a default resov_timeout is 5 minutes, meaning after 5 minutes if it doesn't r receive any repeat alert it will consider the alert stop firing. Sure, you can set "realert" below 5 min in your rules to keep alert fire, but it will affect another alert output. I think the best option is we can keep that timeout configurable in the rules, like this :\

alertmanager_alertname: "freq_alert" 
alertmanager_resolve_timeout: 5 # it will affect end_time - aka time to live - of each alert sent to alertmanager.

Users who config the rules can be aware of this config and expect the right behavior for alertmanager.

[eveningcafe]

@jertel

[nsano-rururu]

Please add alertmanager_resolve_timeout to the documentation. If there is a default value, please also provide the default value.
https://github.com/jertel/elastalert2/blob/master/docs/source/ruletypes.rst#alertmanager

Please use the validation check setting of alertmanager_resolve_timeout
https://github.com/jertel/elastalert2/blob/master/elastalert/schema.yaml#L321

alertmanager_resolve_timeout: {type: integer}

[nsano-rururu]

Please add test code for alertmanager_resolve_timeout
https://github.com/jertel/elastalert2/blob/master/tests/alerters/alertmanager_test.py

[nsano-rururu]

Please update CHANGELOG.md

[eveningcafe]

ok I'll do it now. ~ chotto matte. But the ideal ok right?

[jertel]

Hello @eveningcafe: Are you planning to continue this PR? If so I'll leave it open for a couple more weeks. Let us know.

Thanks!

[eveningcafe]

oh yes, sorry. I'll do. please leave it open

[nsano-rururu]

@eveningcafe

Are there minimum and maximum values for alertmanager_resolve_timeout settings?

[eveningcafe]

Hey guys, how does mock build respose of my request to 'http://alertmanager:9093' ? Here

Sorry, I'm new to mock and currently failing some unit tests. :(

[jertel]

I refactored your implementation to make it a non-breaking change, and to utilize a consistent time configuration, similar to timeframe and buffer_time. Also added a unit test.