Use main branch from calibreapp/image-actions and run on schedule

[yubiuser]

What does this PR aim to accomplish?:

Use main branch from calibreapp/image-actions as it contains updates compared to their latest, outdated tagged version

Ref:
https://github.com/calibreapp/image-actions?tab=readme-ov-file#-usage
https://github.com/calibreapp/image-actions/tags

---

By submitting this pull request, I confirm the following:

1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code and I have tested my changes.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)
6. I have checked that another pull request for this purpose does not exist.
7. I have considered, and confirmed that this submission will be valuable to others.
8. I accept that this submission may not be used, and the pull request closed at the will of the maintainer.
9. I give this submission freely, and claim no ownership to its content.

---

• I have read the above and my PR is ready for review. Check this box to confirm

[netlify]

✅ Deploy Preview for pihole-docs ready!

Name	Link
🔨 Latest commit	6b43632
🔍 Latest deploy log	https://app.netlify.com/sites/pihole-docs/deploys/675ffb9ad074160008ea3242
😎 Deploy Preview	https://deploy-preview-1144--pihole-docs.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[yubiuser]

Some day there might be a new release: calibreapp/image-actions#283

[yubiuser]

Do we want to run this on all PRs or keep the current behaviour?

docs/.github/workflows/calibreapp-image-actions.yml

Lines 5 to 9 in 448e7b4

	paths:
	- '**.jpg'
	- '**.jpeg'
	- '**.png'
	- '**.webp'

We might be able to re-compress existing images if the action changes their compression algortihm.

[yubiuser]

I added a commit following their example (https://github.com/calibreapp/image-actions?tab=readme-ov-file#combined-workflow) to run this on schedule and open a PR if needed. I only changed the action used to create the PR, omitting peter-evans and using gh cli tool instead. We already use this in the other repos
https://github.com/pi-hole/web/blob/5c8945c81c98f6f17e5c138ffbfdcb0831e5a062/.github/workflows/sync-back-to-dev.yml#L16