RTC-520 add notifications: PeerAdded, PeerDeleted

[Rados13]

Acknowledging the stipulations set forth:

• I hereby confirm that a Pull Request involving updates to the Software Development Kit (SDK) has been smoothly merged, currently awaits processing, or is otherwise deemed unnecessary in this context.
• I also affirm that another Pull Request, specifically addressing updates to the documentation body (commonly referred to as 'docs'), has either been successfully incorporated, is in the process of review, or is considered superfluous under the prevailing circumstances.

Blocked by: fishjam-dev/protos#18
Elixir SDK PR
Python SDK PR

[codecov]

Codecov Report

Merging #183 (95c4ce8) into main (69e3a61) will increase coverage by 0.06%.
The diff coverage is 84.61%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #183      +/-   ##
==========================================
+ Coverage   86.85%   86.91%   +0.06%     
==========================================
  Files          74       74              
  Lines        1491     1498       +7     
==========================================
+ Hits         1295     1302       +7     
  Misses        196      196              

Files	Coverage Δ
lib/jellyfish/event.ex	87.87% <100.00%> (+0.78%)	⬆️
lib/jellyfish/room.ex	80.27% <100.00%> (-0.14%)	⬇️
lib/jellyfish/room/state.ex	87.89% <80.00%> (+0.48%)	⬆️

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