Support header checksum

[TingDaoK]

Issue #, if available:

• Adding support for providing checksum in the header instead of trailer.
• CRT will read the body into memory and calculate the checksum directly from the memory in this case, and add it to the header of the request instead of trailer

Description of changes:

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

Attention: Patch coverage is 88.63636% with 5 lines in your changes missing coverage. Please review.

Project coverage is 89.69%. Comparing base (1670150) to head (8f54ef1).

Files with missing lines	Patch %	Lines
source/s3_request_messages.c	88.63%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #454      +/-   ##
==========================================
- Coverage   89.69%   89.69%   -0.01%     
==========================================
  Files          20       20              
  Lines        6145     6172      +27     
==========================================
+ Hits         5512     5536      +24     
- Misses        633      636       +3     

Files with missing lines	Coverage Δ
source/s3_client.c	90.31% <ø> (+0.15%)	⬆️
source/s3_request_messages.c	74.77% <88.63%> (+0.85%)	⬆️

... and 1 file with indirect coverage changes