Automated RPM packaging of AWS CLI v2 using GitHub Actions

Only EL7 (RHEL, Centos, ???) are supported now, but other distros are in the wishlist.

1. ./check_for_new_installer - download the installer and update various metadata files
2. ./respecit - update the spec file to match the downloaded version
3. docker-compose build builder - create the builder image
4. docker-compose run builder ./rebuildit - rebuild the RPM
5. docker-compose run tester ./retestit - test installing the RPM

This should result in:

• no-source RPM: SRPMS/awscliv2-${VERSION}-${RELEASE}.el7.nosrc.rpm
• installable RPM: RPMS/x86_64/awscliv2-${VERSION}-${RELEASE}.el7.x86_64.rpm