Permission checks are done per-job, not per-installation

[lachmanfrantisek]

This task is to not do any permission check right after the Packit service setup but to do it on a job-level basis.

Why?

• We already have a few job-only checks.
• We don't need to require permissions that are not relevant when a user doesn't use a particular job.
• For GitLab, the automatic FAS mapping after the installation does not work => we need to handle this somehow. (Related to "Approval" section in docs not applicable for Gitlab upstreams #1707 )
• Requirements can be more easily documented and the reasoning is easier to provide.

TODO:

• Implement blocklisting mechanism #1964 (:exclamation: high priority)
• Implement user/namespace/project usage metrics #1990 (:exclamation: high priority)
• Based on the measured data set the user/namespace/project limits #2052 (:exclamation: high priority)
• Permission checks are done per-job, not per-installation #1850 (lowe priority)
• Document the requirements for using Packit jobs packit.dev#620 (low priority)
• Change the permission checks to be done per-job #1965 (low priority)

[lbarcziova]

Output from Packit 2023/Q1 planning meeting:

• What's the benefit?
  easier, clearer installation for the users; better UX in general

• Who will benefit?
  all (new) users

[lachmanfrantisek]

After a team discussion, we didn't pick this as a top Packit team priority for the next quarter and preferred epics with bigger user benefits. (Sadly, we have limited resources.) If anyone wants to help us with this, we will be really glad. We are open to any collaboration and have successfully implemented/started multiple affords thanks to people outside of the Packit team.