install: Use RHEL repo for Rocky Linux

[neitsab]

86f94af added Rocky Linux as a recognized distro and thus the script sets up the repo0. However the repo doesn't currently contain the required packages, and thus the installation fails.

Rocky being fully compatible with RHEL, using its repo leads to a working installation. This aligns with the current advice from Rocky's own docs1.

Fixes #264 #373 #468 #469

- What I did

Add a test changing the value of $repo_file_url when rocky is detected to use rhel repo instead.

- How I did it

Thinking a bit and writing as much

- How to verify it

By reading the code?

- Description for the changelog

install: improve Rocky Linux support

- A picture of a cute animal (not mandatory but encouraged)

[thaJeztah]

I'm not sure we should do this; we deliberately don't handle most derivatives; raspbian is the only exception as we migrated that, but adding other derrivatives has proven to become a sliding slope where things "may" work, but also often just enough differences for things to subtly fail.

The plan is to provide add packages for Rocky, but not all are available yet, so wondering if we should either leave the script as-is, or adding a warning ( + delay?) to allow the user to cancel the script.

Any thoughts, @vvoland ?

[neitsab]

TBF this is just a workaround so as not to leave the current situation broken; IMO the script had better state Rocky was unsupported until the repo was effectively setup, and only then 86f94af would have made sense.

I drafted this PR because the replies to my comment on this commit invited to do so, but it is definitely a not-ideal workaround.

The plan is to provide add packages for Rocky, but not all are available yet

This is indeed the root cause and the first issue I wanted to report, but I couldn't find where to do do so (my question below the aforementioned commit didn't get a reply). It would indeed make more a lot more sense to finish building up the packages if that's planned/in doing and then have 86f94af.

Leaving the script as-is results in a less-than-satisfying user experience:

• user runs the script on Rocky
• script sets up a repo but then fails downloading the packages from it
• user thinks official Docker convenience script is broken
• user opens an issue.

That's basically me yesterday, and might generate a bit of useless fuss.

[vvoland]

This will break docker sbx installation which supports Rocky 8: https://github.com/docker/sbx-releases

Official Rocky packages for Docker Engine/CLI are in the works and should be available soon, so I think it's just not worth the time to bother with such workarounds.

[neitsab]

Official Rocky packages for Docker Engine/CLI are in the works and should be available soon

That's great to here, but until then I still think 86f94af should be reverted to avoid the making the install script fail due to the absence of packages in the added repo.

Feel free to close this PR then :-)