automation: adding dependabot for github actions

[gordonkoehn]

Dependabot itself already implements the functionality to keep GitHub actions up to date.

This PR implements a minimal viable dependabot workflow to update:

• Github Actions only
• on a weekly basis
• pointing the PR to our dev branch rubicon
• Call the commit message Github Actions: <<action updated>>

Optinally, we may want to labels to the workflow to add labels to the PR (we'd have to add these to the repo)

    labels:
      - "dependencies"
      - "github-actions"

PR Overview

This PR adds a Dependabot configuration to automatically update GitHub Actions on a weekly schedule with updates merged into the "rubicon" branch.

• Added a new workflow file (.github/workflows/dependabot.yml) that configures Dependabot to target GitHub Actions updates, set a weekly schedule, and customize commit messages.
• The commit message is configured with a prefix that supports additional scope information.

Reviewed Changes

File	Description
.github/workflows/dependabot.yml	New Dependabot workflow file for automating GitHub Actions dependency updates

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ BASH	shellcheck	13		0	1.24s
✅ DOCKERFILE	hadolint	1		0	0.31s
✅ JUPYTER	jupyfmt	12	9	0	8.51s
✅ MARKDOWN	markdownlint	17	3	0	2.24s
✅ PERL	perlcritic	1		0	1.52s
✅ PYTHON	black	53	1	0	2.6s
✅ SNAKEMAKE	snakefmt	25	2	0	11.06s

See detailed report in MegaLinter reports