Bypass for CreateSession reqeust

[TingDaoK]

Issue #, if available:

• Fix the issue where too many request being prepared just waiting to be signed, while we need to make another CreateSession request from the same client to sign the requests.
• So, the requests will block the CreateSession to be made and hang

Description of changes:

• Bypass the throttle on client for CreateSession request, so that it will always get scheduled to be sent

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Merging #384 (fcda93b) into main (ecd0143) will increase coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #384      +/-   ##
==========================================
+ Coverage   88.58%   88.59%   +0.01%     
==========================================
  Files          21       21              
  Lines        5938     5944       +6     
==========================================
+ Hits         5260     5266       +6     
  Misses        678      678              

Files	Coverage Δ
source/s3_client.c	88.01% <100.00%> (+0.05%)	⬆️
source/s3express_credentials_provider.c	92.23% <100.00%> (+0.01%)	⬆️

[waahm7]

A bunch of trivial comments; feel free to merge and we can agonize over names later, maybe.