Bump Lightning Cloud to 0.5.7

[krshrimali]

What does this PR do?

Making threadpool non default from LightningCloud client. (cc: @hhsecond)

Does your PR introduce any breaking changes? If yes, please list them.

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Did you have fun?

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cc @Borda

[tchaton]

LGTM !

[codecov]

Codecov Report

Merging #14757 (8f26a47) into master (e113d38) will increase coverage by 1%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #14757     +/-   ##
=========================================
+ Coverage      84%      85%     +1%     
=========================================
  Files         395      328     -67     
  Lines       28805    25771   -3034     
=========================================
- Hits        24087    21853   -2234     
+ Misses       4718     3918    -800