Create a versioning strategy for the privacy notice and homeserver terms

The legal team would like to be able to link to old versions of the privacy notice and homeserver terms.

Technically we could just point to old revisions on GitHub, but that's a bit barebones. We can come up with a strategy to always have the latest document at the same URL, and link to older revisions.

What I have in mind is something along the lines of [matrix.org/legal/privacy-notice](http://matrix.org/legal/privacy-notice) for the latest document, and something like [matrix.org/legal/privacy-notice/2023-01-17](http://matrix.org/legal/privacy-notice/2023-01-17) for older revisions, with a big warning that people are looking at an old revision.

Legal has identified this as a low priority.

Start by reviewing how the privacy notice and homeserver terms are currently published on matrix.org, then compare that with the proposed latest and dated URLs. Done means the latest document remains available at a stable URL, older revisions have dated links, and old pages clearly warn readers that they are viewing an outdated revision.

Written by the indexing model from the issue text.