Draft: Add tag links

BUG 475303

Needs testing, but this should support tag links. cc @redstrate to test it.

(we kept running into unrelated issues that prevented us from testing locally...)

helpful test link: https://fedi-to.net/go?h=0&target=web%2Bap://tag:FediLinks@example/ (wrapped in fedi-to.net so it works in gitlab)