Add jira notifier / integration of jiralert

[jkroepke]

What did you do?

I would like to integrate a JIRA notifier into AlertManager.

What did you expect to see?

A native Atlassian Jira integration

What did you see instead? Under which circumstances?

Currenty, adapter is needed to create JIRA issues from AM. (https://github.com/prometheus-community/jiralert)

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Before starting to develop such an integration into AM, I would like to ask if the maintainers are open for such an integration.

Currently, I able to find 5 year old comments (https://github.com/prometheus/alertmanager/pull/1012#pullrequestreview-67829943) which seems like an NO

An actual statement would helpfull to get the directory, if jiralert should be the focus or the integration into AM.

[bwplotka]

We discussed this internally and indeed it's an option, but we were looking for maintainers: https://github.com/prometheus-community/jiralert/issues/145

[gotjosh]

Thanks, both @bwplotka and @jkroepke -- I think that about ~300 stars, is the right level of support that we would consider to include in the core of the Alertmanager. I have assigned myself to take a look at the PR at my earliest convenience.