expose m.reaction power level to room PL settings by default

[HarHarLinks]

Your use case

What would you like to do?

manage my announcement room to only allow mods to post messages but anyone to send reactions, like Element Web Announcements and Synapse Announcements.

to do that, I need to set message PL > default, reaction PL <= default and redaction PL <= default

How would you like to achieve it?

add m.reaction to room settings -> permissions

Have you considered any alternatives?

it might be useful to have some presets like "announcement room, users can only react" which sets message = mod, reaction = redact = default

Additional context

element-hq/element-meta#1385 is closely related

[saibotk]

While #7492 added a settings switch, this still leads to weird UX, where Users can send reactions but are not allowed to remove them.

[HarHarLinks]

You are correct, #7492 misses the fact that m.room.redaction must be exposed alongside it (so you can redact your own messages, which can only be reactions since that's the only you're allowed to send).
@t3chguy please re-open.

I have split off my other suggestion of even more proper UX to element-hq/element-meta#308 to be addressed independently.