[CIS-1079] Fix CoreData misuse when creating Direct Messaging channels

[b-onc]

CoreData entities should be accessed from their own queues only.

Resolves #1336

[codecov-commenter]

Codecov Report

Merging #1337 (8cda2c5) into main (a5efc29) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1337      +/-   ##
==========================================
- Coverage   91.21%   91.16%   -0.06%     
==========================================
  Files         227      227              
  Lines        9767     9768       +1     
==========================================
- Hits         8909     8905       -4     
- Misses        858      863       +5     

Flag	Coverage Δ
llc-tests	91.01% <100.00%> (+<0.01%)	⬆️
llc-tests-ios12	87.76% <100.00%> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...trollers/ChannelController/ChannelController.swift	92.24% <100.00%> (+0.01%)	⬆️
...eamChat/APIClient/Endpoints/Payloads/RawJSON.swift	83.33% <0.00%> (-11.91%)	⬇️

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[SagarSDagdu]

LGTM 🚢

[DominikBucher12]

⛴🇮🇹