Support PowerPC architecture for sigv4 signature (#1847)

* Use hmac and sha2 instead of ring on powerpc

* Enable aws-sig-auth in CI

* Update CHANGELOG

* Run tests against exotic platforms

* Run tests only against aws rust runtime

* PowerPC 32 and 64 bit should be fully testable now

* Maybe this time build and test will work

* Add licence header to hmac.rs

* Properly use finalized_fixed

* Revert leftover

* Temporary disable crc32c test on powerpc

* Temporary disable system_time_conversion_test on 32bit CPUs

* Disable other 3 tests on 32bit

* Temporarily disable last test

* Update CHANGELOG and document TODOs with issues

* Run aws-smithy-client tests in CI with crosscompiled local openssl

* Simplify CI script

* Use correct curl options

* Use the right OS for i686

* Looks like I finally foung the right os type for i686

* Add `tcp` feature to `hyper` to get tests compiling.

* Enable verbose logging to debug CI failure in cross.

* Use pre-built openSSL on i686

* Fix empty spaces.

* Set environment variables based on matrix.target

* Remove all usages of `ring` from `aws-sigv4`. It ensures broader platform compatibility and higher performance.

* Update changelog entries.

* Remove redundant dev dependencies.

Co-authored-by: Luca Palmieri <20745048+LukeMathWalker@users.noreply.github.com>