CI/releases: build and release Rocky Linux RPM packages

What

CentOS has been deprecated and no longer developed. Two other distributions emerged as valuable alternative to CentOS: rockylinux and Almalinux.

Both promise to maintain compatibility with RHEL distributions.

I chose in this MR rockylinux as the second supported distribution for our rpm packages.

Why

Rockylinux has today a larger use-base.

How

I've added a rockylinux 9.3 in the CI to make sure our rpm packages can always be compiled on this platform.

Since rockylinux uses a different set of repositories then fedora, the installation script must account for this discrepancy. Also opam is not available on rockylinux and we have to install it manually.

Fix: #6770 (closed)

To make this possible I've also added the matrix construct for CIAO

Manually testing the MR

Run the manual job to build the rpm packages and make sure they compile.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR