Add Rocky Linux support to cloud-init

[nazunalika]

Proposed Commit Message

summary: Add support for Rocky Linux

Rocky Linux is a RHEL-compatible distribution so all changes that have
been made should be trivial.

Additional Context

https://rockylinux.org

We currently have RC1 out (for version 8.3) and currently working on 8.4. We
had to redo our patches for 8.4 as it was rebased. We realized an upstream PR
was not made for our distribution, hence this submission.

Please let me know if I made a mistake anywhere throughout this PR and I
will try to correct it.

Thank you!

Test Steps

Checklist:

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly

[TheRealFalcon]

Thanks for this submission. Overall this looks good. A few notes...

Most of the lists you added rocky to were in alphabetical order. Instead of adding rocky to the end of the list, can you add it to keep the ordering alphabetical?

One of the unit tests you wrote is failing on CI. It's because of the parsing of /etc/redhat-release is expecting a codename after the version number. Would it be possible to update the implementation to make the codename optional?

I suggested a change inline for the other failing unit test.

[nazunalika]

I believe I addressed the alphabetical order lists and also the code name. We added a code name recently but I didn't provide an updated set of info. Hopefully that addressed that issue there. I couldn't find your suggestion in the modified file list. Or perhaps I've looked in the wrong place.

[TheRealFalcon]

Hmmm, weird...must have put that suggestion in a different tab then I closed or something. Should be here now.

[TheRealFalcon]

This is checking that the list in cc_ntp.py matches some documentation output. Unfortunately, it hasn't been updated in a while, but this should fix it.

Suggested change

	('**Supported distros:** almalinux, alpine, centos, debian, '
	'fedora, rocky'),
	('**Supported distros:** almalinux, alpine, centos, debian, '
	'fedora, opensuse, rhel, rocky, sles, ubuntu'),

[TheRealFalcon]

Looks good now, thanks!