Archive 2021 and make latest point to 2022

Soon, TeXlive 2022 will be released and the 2021 version will be archived. We should prepare for this now so that on release date, we can successfully switch to the 2022 version.

From [tug.org/texlive]

Plan for TeX Live 2022:
15feb: candidate/final sources committed, test builds begin.
27feb: tlpretest starts, CTAN updates continue there and in tlnet.
10mar: code freeze for final build, major bug fixes only.
22mar: final updates from CTAN, final doc tweaks.
23mar: deliver TL image for TeX Collection packaging/testing.
1apr: deliver TeX Collection DVD image for manufacturing.
3apr: public release (also of MacTeX).
June?: delivery of DVDs to members.