[Feature Request]: Automate / validate changelog area mappings

### Prerequisites

- [x] I have searched existing issues to ensure this feature hasn't already been requested
- [x] I have tested using the latest version of docs-builder

### What problem are you trying to solve?

Per https://github.com/elastic/elasticsearch/pull/140141/changes#r3221759284, for teams that have PR/issue labels that change fairly frequently there's a manual step required to ensure the changelog configuration file's `pivot` settings are up-to-date. Otherwise, the changelog fields can't be derived and must be added by contributors manually.

### Proposed Solution

Per https://github.com/elastic/elasticsearch/pull/140141/changes#r3221759284, do teams need some kind of process that will automatically update the changelog configuration file's `pivot.areas`? Sounds like Elasticsearch might already have something like this in their old changelog system.

Alternatively, if a team decides that lack of an area label is a failure, making this a configurable validation check in the [changelog action](https://github.com/elastic/docs-actions/blob/main/changelog/README.md#how-it-works) and/or [evaluate-pr command](https://elastic.github.io/docs-builder/cli/changelog/evaluate-pr/) might suffice.

### Examples and Research

_No response_

### Alternative Solutions

_No response_

### Additional Context

_No response_

### How important is this feature to you?

Nice to have