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Use main branch from calibreapp/image-actions as it contains updates compared to their latest, outdated tagged version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

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[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

[XhmikosR]

TBH, this doesn't seem to even come close to the compression one can get with other scripts/tools. Unfortunately, I've yet to find an automated way for this, but I can submit a PR later which compresses the images as good as I can get them to compress.

[yubiuser]

Sure, go ahead