Add a precommit to detect when docs have been moved

### Body

This is useful when we move over / rename docs and miss adding those in redirects.txt leading to trouble later for external links.

Adding a precommit will catch hold of a good chunk of those.

### Committer

- [x] I acknowledge that I am a maintainer/committer of the Apache Airflow project.

Start by inspecting redirects.txt and the repository's pre-commit configuration. The check should identify moved or renamed documentation that lacks a corresponding redirect entry, and the work is done when the pre-commit catches those omissions.

Written by the indexing model from the issue text.