aws_sigv4: fix header computation

aws_sigv4: fix header computation

Handle canonical headers and signed headers creation as explained here:
https://docs.aws.amazon.com/general/latest/gr/sigv4-create-canonical-request.html

The algo tells that signed and canonical must contain at last host and
x-amz-date.

So we check whatever thoses are present in the curl http headers list.
If they are, we use the one enter by curl user, otherwise we generate
them.  then we to lower, and remove space from each http headers plus
host and x-amz-date, then sort them all by alphabetical order.

This patch also fix a bug with host header, which was ignoring the port.

Closes #7966