[Alerting V2] Rotate a rule's API key with the new Update API key action

## Summary

Alerting V2 rules now have an Update API key action, available as a single-rule action (rule details page and rules list row actions) and as a bulk action from the rules list. Invoking it regenerates the API key the rule executor uses to query Elasticsearch, using the current user's credentials and privileges, without requiring a full edit-and-save of the rule. The action is disabled for disabled rules, and the rule's enabled state and schedule interval are preserved.

**Why this needs docs:** New menu action confirmed via i18n-labeled 'Update API key' entries in both the single-rule actions menu and the rules bulk actions component; this adds a new, faster remediation path for a problem (stale rule API key) that the authorization docs currently describe only one way to fix.

## Resources

- PR [#281337](https://github.com/elastic/kibana/pull/281337) — [Alerting V2] Add "Update API key" action (single + bulk) for rules

Screenshots from PR


## Availability

| Channel | Details |
|---------|---------|
| **Stack** | v9.6.0 |
| **Serverless** | Aug 17–Aug 21 |
| **Feature status** | preview |
| **Feature flag** | None — active by default |

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*Created with [Docs Quest Scanner](https://github.com/florent-leborgne/docs-quest-scanner) by @nastasha-solomon*

## Suggested edits

[Rule, action policy, and workflow authorization in the experimental alerting system](https://www.elastic.co/docs/explore-analyze/alerting/experimental-alerting-system/authorization) > Check and fix authorization errors
- **What the docs say:** Error type: Stale or not valid API key. Cause: The stored key is no longer valid... How to resolve it: Refresh the key by saving the rule again or toggling it off and back on.
- **What to add:** The listed remediation only mentions re-saving or toggling the rule. Add that rules now also have a dedicated Update API key action (single, from the rule's actions menu on the details page or rules list; or bulk, from the rules list) that regenerates the key directly without a full edit. Applies from 9.6.0 and in serverless.