Change the permission checks to be done per-job

[lbarcziova]

• Update the code (follow the document with the requirements)
  • the check_and_reportshould mainly check the blocklist
  • other checks can be moved to the handler pre-checks as we have e.g. for internal TF check here
• Update the content of the GitLab issues we create on installation, GitHub issues created in the notifications repo and GitHub app installation information (link the docs created in packit/packit.dev#620, for GitHub, we may use this link as forward URL after installation)
  • clearly state that the verification is not needed for all jobs

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Part of packit/packit-service#1850 epic.