Build an Omnibus package for Amazon Linux 2 and officially provide support

We are getting increasing demand for Amazon Linux 2 support. Unfortunately, compatibility through EL7 is not guaranteed as the kernel versions have diverged.

As part of this issue we should:

1. Validate whether GitLab works on Amazon Linux 2
2. Determine effort to support Amazon Linux 2
3. Add Amazon Linux 2 to our support matrix, and create automated builds going forward
4. Create Amazon Linux 2 RPMs for both x86 and ARM (AWS is on a very strong ARM push in terms of savings, performance and sustainability)
5. Update script.rpm.sh to not set Amazon Linux 2 to point to EL7 X86 - but the proper distro and architecture RPM.

Notes:

• packages that are in the amazon linux 2 extras repo should be preferred over other sources for the same packages. It has it's own command amazon-linux-extras. See here for more: https://aws.amazon.com/premiumsupport/knowledge-center/ec2-install-extras-library-software/