Put note on matrix groups about Reps decomission

[couci]

Goal:

Add a note on all matrix groups that the reps program is decomissioned

Required:

• [x] #449
• [x] Add note on reps review (owner @couci )
• [x] Add note on reps group (owner @plwt )
• [x] Add note on council group (owner @plwt )
• [x] Add note on reps announcement (owner @couci )

[Timmaks]

I all ready did for the mentor, reps and announce group: The Reps program is retired at 01-09-2023, see https://discourse.mozilla.org/t/important-announcement-decommissioning-of-the-mozilla-reps-program/122291 for more info

[Timmaks]

Did not meant to open a new issue, I am on mobile and did something wrong...

[plwt]

Council room updated.

[couci]

Thanks everyone