nixos/bluesky-pds: prefer goat & add rate limit by deafult
see
https://github.com/bluesky-social/pds/commit/65c9efc6d5177141552136a7e51b1ac9413cb889
and
https://github.com/bluesky-social/pds/commit/9a72155fee4e7e1de0e0add5454c5571b89e05e0
(cherry picked from commit 35b20dfd9ec9a4d8953ffd8877e8c82b801b5bf7)