Reactions in relay groups: warn that they are not relayed outside

[missytake]

Reactions should be relayed as well, and removing reactions should also be relayed.

[missytake]

challenges:

• relay a reaction from the relay group to the outside chat is fine; if another group member reacts differently, the most recent reaction should be relayed I guess. Unfortunately relay group members won't be able to judge which reaction was the final one. I don't see a good workaround; the status quo that relay group members don't know that the bot will ignore the reaction is worse for sure.
• if the outside chat is a group, there could be multiple reactions to a message of the bot; but the bot can only react once to a message.

[missytake]

Let's not relay reactions to the outside, it will not work nicely in many environments. Instead the bot should reply to a relay group that it doesn't relay reactions outside.