ci: Fix Development Freeze Automation

ci: Fix Development Freeze Automation

Due to the limitation of `GITHUB_TOKEN` when running workflows from forks,
it's required to split the `development_freeze` workflow in two.

* First workflow will run on the `pull_request` trigger and save the PR
number in the artifact. This workflow is running with read-only permissions
on `GITHUB_TOKEN`.
* Second workflow will get triggered on `workflow_run`. It will be run
directly in the `systemd/systemd` context and can get permission to be
able to create comments on PR.

GITHUB_TOKEN limitations:

* https://docs.github.com/en/actions/security-guides/automatic-token-authentication#permissions-for-the-github_token

GitHub Security Labs Article - How to correctly and safely overcome GITHUB_TOKEN limitations:

* https://securitylab.github.com/research/github-actions-preventing-pwn-requests/