Add lobby tournaments update subscription

[solar05]

Fixes #1088

[codecov-commenter]

Codecov Report

Merging #1141 (a802b73) into master (a13918a) will decrease coverage by 0.08%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master    #1141      +/-   ##
==========================================
- Coverage   73.58%   73.49%   -0.09%     
==========================================
  Files         130      130              
  Lines        2612     2615       +3     
==========================================
  Hits         1922     1922              
- Misses        690      693       +3     

Impacted Files	Coverage Δ
...s/app/lib/codebattle_web/channels/lobby_channel.ex	80.64% <33.33%> (-5.07%)	⬇️
...es/app/lib/codebattle_web/channels/game_channel.ex	83.67% <0.00%> (-2.05%)	⬇️

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