Add applies_to tags to recent workflows/Agent Builder docs changes

https://github.com/elastic/docs-content/pull/5630 was approved by a tech writer who forgot to check if the changes were bug fixes or changes in 9.4/serverless. It was indeed the latter so, in the spirit of [cumulative docs](https://www.elastic.co/docs/contribute-docs/how-to/cumulative-docs), we need to rectify that with applies_to tags instead of just editing the page.

The page needs to remain relevant for 9.3 and 9.4 users. Refer to https://github.com/elastic/elastic-docs-skills/blob/main/skills/authoring/applies-to-tagging/SKILL.md for deets.