Write Vale rules for the new alert icons in docs

In &5020 (closed), we decided to use only two alerts (note, warning), and eliminate any bold text coming after the icon.

This issue is about:

1. Writing a Vale rule to check for any CAUTION/DANGER/TIP occurrences and fail if those are found. The link to the docs will be https://docs.gitlab.com/ee/development/documentation/styleguide/index.html#alert-boxes once updated.
2. Writing a Vale rule to check for any NOTE: **Note:**/WARNING: **Warning:** occurrences and fail if those are found. The link to the docs will be https://docs.gitlab.com/ee/development/documentation/styleguide/index.html#alert-boxes once updated.

The Vale rule will need to be added to all 4 products:

• GitLab
• Omnibus
• Runner
• Charts