Host last two major versions on Archives site

• Adds the 13.12 and 14.10 sites to archives.docs.gitlab.com.
• Removes logic in the version picker to link the last majors to docs.gitlab.com. By hosting the last major releases here, we no longer need to set the base URL for links conditionally (it will always be the current site, archives.docs.gitlab.com).

This is a step towards closing #20 (closed).

Test locally

1. Check out this branch
2. Make sure you have up-to-date node modules: npm i
3. Turn on the dev server: npm run dev
4. Use the version selector to try a few different versions. While the links won't work locally (because the older versions probably do not exist on your local environment), you should get paths for each version like this: https://localhost:5174/xx.yy where xx.yy = the selected version.