Update release docs script with navigation data changes

[gracegrimwood]

Some updates are required to the release docs script due to the nav changes in #115, which is not merged yet but will be once these changes are made (otherwise we'll break the docs navigation dropdown the next time we run a release).

The specific compatibility issues arise from these changes in _data/kroxylicious.yml:

1. Adds new base-level data structures (the older_versions bit)
2. Adds a new item to the existing versions structure that isn't a normal release (the - title: 'Archive' entry)
3. Adds extra metadata to some of the items in versions (the development: true and archive: true bits)

And the changes needed to the release docs script for each of these are:

1. The script needs to move old items from versions into older_versions (so that the nav dropdown doesn't just fill back up with newer releases, and so that we don't have to do this manually), so the script needs to locate the last actual release item in the versions list, then locate the start of older_versions and move it to the top of that
2. The script needs to not move the archive entry under any circumstances (or we won't be able to navigate to it or any of the docs pages it contains, unless we type the URL manually)
3. The script currently uses the end of the - title: 'Development' entry to find where to insert the new release entry into this file (so that it appears in the nav dropdown), but the end of this entry has now changed so we have to update how we're doing that (<- this is the easiest of the changes)