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

[](https://app.codecov.io/gh/awslabs/aws-c-s3/pull/384?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=awslabs) ```diff @@ 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](https://app.codecov.io/gh/awslabs/aws-c-s3/pull/384?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=awslabs) | Coverage Δ | | |---|---|---| | [source/s3\_client.c](https://app.codecov.io/gh/awslabs/aws-c-s3/pull/384?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=awslabs#diff-c291cmNlL3MzX2NsaWVudC5j) | `88.01% <100.00%> (+0.05%)` | :arrow_up: | | [source/s3express\_credentials\_provider.c](https://app.codecov.io/gh/awslabs/aws-c-s3/pull/384?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=awslabs#diff-c291cmNlL3MzZXhwcmVzc19jcmVkZW50aWFsc19wcm92aWRlci5j) | `92.23% <100.00%> (+0.01%)` | :arrow_up: |