Add an action to trigger Dependabot updates

[artembilan]

Dependabot has some limitations:

1. The dependabot.yml has to be on a default branch with all the supported branches configs: https://docs.github.com/en/code-security/concepts/supply-chain-security/about-the-dependabot-yml-file#where-to-store-the-dependabotyml-file
2. There is no official API to trigger Dependabot manually, e.g. just before release we would like to have everything up-to-date: Manually trigger an update for a specific dependency dependabot/dependabot-core#2980. As that issue states and what we know from our experience, we have to go to the Insights -> Dependency Graph -> Dependabot and click Check for updates on every package-ecosystem for all the supported branches (pulled from the mentioned dependabot.yml).

One of the nice workaround suggested by the community is to make a change to the dependabot.yml file which becomes a trigger for Dependabot scan to run.

I wrote the following GHA Workflow and tested it against real project:

name: Trigger Dependabot Updates

# This workflow is a convenient alternative to the GitHub UI interface for Dependabot updates.
# The workflow performs Toggle executable permission as a superficial change on the dependabot.yml file.
# That is enough for Dependabot to understand that some changes have happened in the dependency updates config.

on:
  workflow_dispatch:

jobs:
  trigget-dependabot:
    runs-on: ubuntu-latest
    steps:

      - uses: actions/checkout@v6
        with:
          token: ${{ secrets.GH_ACTIONS_REPO_TOKEN }}
          show-progress: false

      - name: Touch dependabot.yml
        run: |
          file=".github/dependabot.yml"
          # Toggle executable permission as a superficial change
          [ -x "$file" ] && chmod -x "$file" || chmod +x "$file"
          
          git config --global user.name 'Spring Builds'
          git config --global user.email 'builds@springframework.org'
          git commit -am "CI/CD: Trigger dependabot updates"
          git push origin

Would be nice to have it as an action in this repository to be reused whenever we want to avoid manual UI clicks.

Thanks