Ignore Content-Length header when setting 'chunked' for Transfer-Encoding

[jonathan343]

Note: This is the AWS CLI v2 version of boto/botocore#3360

This PR removes the Content-Length header when a request is sent using chunked upload.

See the guidance below from Signature Calculations for the Authorization Header: Transferring Payload in Multiple Chunks for more details

When transferring data in a series of chunks, you must do one of the following:

Explicitly specify the total content length (object length in bytes plus metadata in each chunk) using the Content-Length HTTP header. To do this, you must pre-compute the total length of the payload, including the metadata that you send in each chunk, before starting your request.

Specify the Transfer-Encoding HTTP header. If you include the Transfer-Encoding header and specify any value other than identity, you must omit the Content-Length header.

For all requests, you must include the x-amz-decoded-content-length header, specifying the size of the object in bytes.

[nateprewitt]

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (d413154) to head (7bf89c9).
Report is 11 commits behind head on v2.

Additional details and impacted files

@@    Coverage Diff     @@
##   v2   #9265   +/-   ##
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