[Feature Request]: Support for Footnotes or Fancy Callouts in Tables

### Additional Context

This feature would be beneficial for providing additional context or caveats directly in documentation tables, rather than forcing authors or readers to jump elsewhere on the page. This approach is already adopted in some other documentation ecosystems.

### Alternative Solutions

The workaround is to use inline numbering in tables and describe them in a numbered list afterwards, but this is not user-friendly and can become unwieldy in complex documentation tables.

### Examples and Research

- Example featuring callout annotation in a table: https://www.elastic.co/docs/deploy-manage/tools/snapshot-and-restore#index-compatibility
- Markup pattern from our docs: https://github.com/elastic/docs-content/blob/main/deploy-manage/tools/snapshot-and-restore.md?plain=1#L161-L174
- Callouts in tables are supported in some external tools/documentation sites.

### How important is this feature to you?

"Important"

### What problem are you trying to solve?

Currently, there is no support for including footnotes or special callouts within tables in our documentation, unlike the support for footnotes/code callouts elsewhere. As discussed in internal conversations, the current workaround is to use plain numbers like (1), (2) in the table body, and then explain them later as a numbered list below the table—this is not very elegant or scalable for complex docs.

### Proposed Solution

Add first-class support in docs-builder for table cell footnotes, or the ability to reference callouts/notes directly within table cells (possibly rendered as superscript-style links or tooltip-style annotations). Ideally this would work similarly to how we handle code callouts or like the callout pattern used here: https://www.elastic.co/docs/deploy-manage/tools/snapshot-and-restore#index-compatibility.

### Prerequisites

false,false

[View original Slack conversation](https://elastic.slack.com/archives/C05PP2LEC1X/p1780392896864669?thread_ts=1780392896.864669&cid=C05PP2LEC1X)