Default sticker packs require federation with t2bot.io

[spantaleev]

This is similar to #159. In this case, we don't discuss running without federation, but rather running with restricted federation settings (using federation_domain_whitelist).

Servers that enable federation but only with a whitelist of other servers, also need to whitelist federation with t2bot.io if the default sticker packs are enabled (which they are by default).

I wonder if there's a better way to serve the stickers locally (importing those same sticker packs locally?).. Or perhaps we should indicate this federation requirement somewhere.

[jolly-jump]

Just ran into this and by sheer luck (no brain) tried to whitelist t2bot.io - which worked wonderously.