Update Molecule platform data

[alessfg]

Proposed changes

Note: This PR partially reverts the changes made in #572.

Explicitly specify amd64 as the platform used in the Amazon Linux 2/CentOS/Oracle Linux/RHEL 7/SLES 15 Molecule Docker images. This will ensure that tests work when run on different host architectures (e.g. newer Macbooks with arm64 processors) when running tests in distributions that only support amd64 (either due to lack of support for a cgroups v2 backport or due to lack of builds for arm64).

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• [x] I have read the CONTRIBUTING document
• [x] I have added Molecule tests that prove my fix is effective or that my feature works
• [x] I have checked that any relevant Molecule tests pass after adding my changes
• [x] I have updated any relevant documentation (defaults/main/*.yml, README.md and CHANGELOG.md)