ci: Group Dependabot GitHub Actions PRs

[alessfg]

Proposed changes

This PR groups together the following Dependabot GitHub Actions PRs into two groups:

• Updates to Docker related GitHub Actions
• Updates to official GitHub Actions

This should help reduce both PR spam and ease the Dependabot related maintenance burden.

Checklist

Before creating a PR, run through this checklist and mark each as complete:

• I have read the contributing guidelines.
• I have signed the F5 Contributor License Agreement (CLA).
• If applicable, I have added tests that prove my fix is effective or that my feature works.
• If applicable, I have checked that any relevant tests pass after adding my changes.
• I have updated any relevant documentation (e.g. README.md).