feat: add automated workflows for flake and package updates

[Copilot]

Adds two scheduled GitHub Actions workflows to automate dependency and package updates with PR creation.

Workflows

update-flake.yml

• Runs nix flake update weekly (Monday 00:00 UTC)
• Creates PR when flake.lock changes
• Uses cachix/install-nix-action@v27 with flakes enabled

update-pkgs.yml

• Auto-discovers and updates all RKE2 versions via existing update-script.sh
• Runs weekly (Monday 02:00 UTC)
• Bash strict mode (set -euo pipefail) with failure tracking
• Continues on partial failures, creates PR for successful updates

Implementation Details

Both workflows:

• Check for changes before creating PR (no empty PRs)
• Use peter-evans/create-pull-request@v6 for automation
• Support manual trigger via workflow_dispatch
• Auto-label PRs (automated, dependencies, packages)
• Clean up branches after merge

Example PR creation logic:

- name: Check for changes
  id: check_changes
  run: |
    if git diff --quiet flake.lock; then
      echo "changed=false" >> $GITHUB_OUTPUT
    else
      echo "changed=true" >> $GITHUB_OUTPUT
    fi

- name: Create Pull Request
  if: steps.check_changes.outputs.changed == 'true'
  uses: peter-evans/create-pull-request@v6

Original prompt

Add two cron github action, one automatically update flake, the other automatically update pkgs. Create PR when pkgs or flake is updated.

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