Standardize code from dot to array notation

[alessfg]

Proposed changes

• Standardize code from dot to array notation to keep in with the standards set by the other roles in the Ansible NGINX core collection.
• Bump the minimum version of Ansible core required to run the role to 2.12 (2.11 is no longer supported by Ansible).

Checklist

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

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