[3006.x] Drop CentOS 7 support, and build RPM packages with Rocky Linux 9 container

[ScriptAutomate]

What does this PR do?

• Drop CentOS 7 support
• Replace CentOS Stream 9 container, used for packaging, with Rocky Linux 9

What issues does this PR fix or reference?

• Fixes [TECH DEBT] Drop CentOS 7 due to EOL in June 2024 #66623
• Fixes [TECH DEBT] Switch to Rocky Linux 9 containers for packaging instead of CentOS Stream 9 #66624

Previous Behavior

• Test CI/CD against CentOS 7, and publish packages to RHEL 7 repository paths
• Build RPM packages with CentOS Stream 9 for RHEL-based systems

New Behavior

• No longer test CI/CD against CentOS 7, and no longer publish packages to RHEL 7 repository paths
• Build RPM packages with Rocky Linux 9 for RHEL-based systems

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

Commits signed with GPG?

Yes

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PR Guidelines.

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