Add 'nginx_app_protect_manage_repo' feature flag and defaults

[sjugge]

Proposed changes

This change adds a nginx_app_protect_manage_repo boolean which can be used to disable Nginx App Protect repo management by this role.

This feature flag addresses edge-cases where Nginx' App Protect repositories are managed by other means and should not be configured by this role in order to install Nginx App Protect. The default behavior of the role is unaltered.

Checklist

• 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)

Sidenote on Molecule tests, as a test for setting nginx_app_protect_manage_repo to false would effectively require current tests to be disabled, and as the default behavior is not altered, no additional tests have been added.

[alessfg]

I'm going to copy/paste what I wrote on a similar PR for the NGINX role (nginxinc/ansible-role-nginx#420) if that's fine by you 😝

Minor nitpick, can you rename Nginx to NGINX in comments? Can you update the Changelog too?

Re Molecule tests, you could arguably create a new scenario and setup the NGINX App Protect repo beforehand in the prepare.yml playbook (you can check an example under the plus molecule test and you can probably copy/paste the same tasks found in the role proper to setup the NGINX repository in the prepare.yml playbook). Not necessarily a requirement to merge this PR, but it would be nice.

[sjugge]

@alessfg dito for nginxinc/ansible-role-nginx#420 ;) , CHANGELOG & NGINX naming updated