Split changelog

What does this MR do and why?

Describe in detail what your merge request does and why.

As described in #331794 our changelog is now too big to be rendered, this merge requests archives all the entries for 13.X.Y and 14.X.Y into the dedicated changelogs folder.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.