fix: Avoid requesting the same image more than once [SQSERVICES-1985]

[atomrc]

SQSERVICES-1985 [web] At load time the avatar are downloaded as many times as they are in view

The problem

When the app first loads, when a conversation is displayed there are n avatar requests that are sent at the same time.
Those trigger n actual network request and some of them are targeting the same image.
This ends up in duplicate requests that are hitting backend and eventually putting the webapp in a rate limit state.

The solution

instead of caching the image only when the request is successful, we cache the promise of the request as soon as the request is fired. This way any subsequent request will then get the cached promise and will avoid sending the request on the network

Before

After

[codecov]

Codecov Report

Merging #14924 (453047b) into dev (0727207) will decrease coverage by 0.01%.
The diff coverage is 30.00%.

@@            Coverage Diff             @@
##              dev   #14924      +/-   ##
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- Coverage   42.92%   42.91%   -0.01%     
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  Files         624      624              
  Lines       21320    21322       +2     
  Branches     4899     4899              
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  Hits         9151     9151              
- Misses      11000    11002       +2     
  Partials     1169     1169