feat: add reusable acceptance test workflow

[phil-davis]

This is the "basic" flow that sets up Apache, installs a single or dual-server environment with 1 or 2 owncloud core instances running with the app-under-test set up and enabled. That allows ordinary tests and federated tests to run and pass.

I have tried to pass things in env variables etc, in the same way as was done in the other PRs today that secure the flow from command injection, validate inputs... That will need reviewing to find any holes that I have missed.

In future (next week), the acceptance reusable workflow will need to be enhanced for apps that use more external environment. For example:

• provide a mail server
• provide an LDAP environment
• provide S3 storage (or other back-end storage types), for testing apps that support different storage
• allow running with https (set up certificates...) - we might want to be able to run acceptance tests using https

[phil-davis]

@DeepDiver1975 @jvillafanez this works for activity, admin_audit and impersonate apps.
It probably has enough flexibility for lots of the "ordinary" apps.

Please review. Specially for security loopholes...

And I think that we could merge and use this, and then I can expand its features/options next week to cover more of the "special" apps (things that send email, LDAP, files_primary_s3....). Let me know which "external feature" apps are most important to support first.