Generic issue metadata support in issue alert actions

### Problem Statement

I have an issue alert which covers many different groups of errors. For example, I could have an alert that covers all of my environments. Or an alert that covers multiple browsers, or user operating systems, or a custom tag.

I want my alert to be able to include this information in the actions it generates, so that I can have more information automatically included without needing a manual process. For example, I'd like to add a label to Jira tickets that get created based on a custom tag of the issue that triggered the alert.

#48851 has a related use-case around customizing tickets, although it's more focused on controlling currently unconfigurable aspects of the Jira integration (such as the title or description) via templates, while this issue is more about adding some templating support to the already-configurable fields of actions in general (including Jira).

### Solution Brainstorm

The Slack integration already has this support via the “and show tags” field (note that it lets you specify default fields as well, not only custom tags), which gets included in the slack message

It seems this could be accomplished in all integrations via string templating support, for example allowing to use `{{level}}` or `{{tags.my_custom_tag}}`. This could, for example, allow the Jira integration to use the level, or custom tags, to set labels for the ticket. Or allow customization of github issue creation labels, or any other integration that has string inputs.

### Product Area

Alerts

┆Issue is synchronized with this [Jira Improvement](https://getsentry.atlassian.net/browse/FEEDBACK-2213) by [Unito](https://www.unito.io)