github: code review process improvements

[tarasmadan]

Our PR backlog is continuously growing and we're losing the focus.
The proposal is to speed-up the code review for the ready-for-review PRs.
The PR is considered ready-to review if:

1. It is not stale.
   • github: add stale.yml workflow to label stale PRs #7567
   • github: optimize stale.yml to process all open PRs ascending #7568
2. The tests are passing and there are no merge conflicts.
   • .github/workflows: add well-shaped label management workflow #7565
3. The author wasn't recently asked to do changes.
   • .github: check if CHANGES_REQUESTED is addressed for well-shaped label #7575

Additionally we want to:

1. Make sure all the non-draft PRs have at least 1 assigned reviewer from the core team.
   • github: assign random reviewer on ready_for_review #7576

Github is not storing artefacts for the 90 days old events. This is the reason we mark everything older that 90 days stale.