awx: add requirements.yml for galaxy roles

[sxa]

Some of our roles (curl and GIT_Source) are trying to use things from ansible galaxy - homebrew and zypper specifically - which are not available by default, so they fail from AWX when you try to sync the project.

This configuration file, based on the information in https://docs.ansible.com/ansible-tower/3.8.4/html/userguide/projects.html#ansible-galaxy-support, allows us to use the common modules from Ansible Galaxy. Note that this requires Enable Collection(s) Download to be set on in the Settings -> Jobs Settings section of the UI (Only available to
admin)

Related to #3339 (comment)

Testing at https://awx.adoptium.net/#/jobs/playbook/122/output - since it's got past the initial failure at the start (see below) this should be ok to merge now.

ERROR! couldn't resolve module/action 'homebrew'. This often indicates a misspelling, missing collection, or incorrect module path.
The error appears to be in '/runner/project/ansible/playbooks/AdoptOpenJDK_Unix_Playbook/roles/curl/tasks/main.yml': line 121, column 3, but may
be elsewhere in the file depending on the exact syntax problem.
The offending line appears to be:
- name: Install latest version of curl for MacOS
  ^ here

Checklist

• commit message has one of the standard prefixes
• faq.md updated if appropriate
• other documentation is changed or added (if applicable)
• playbook changes run through VPC or QPC (if you have access)
• VPC/QPC not applicable for this PR
• for inventory.yml changes, bastillion/nagios/jenkins updated accordingly

[steelhead31]

LGTM