Support MicroShift V4.16 on RHEL 9.4

Feature Overview (aka. Goal Summary)  

OCP 4.16 is switching to RHEL 9.4 (EUS release) . Hence MicroShift needs to switch, too.

MicroShift V4.16 will be supported only on RHEL 9.4. 

Goals (aka. expected user outcomes)

Requirements (aka. Acceptance Criteria):

1. Support MicroShift V4.16 on RHEL 9.4 X86 and ARM
2. Older MicroShift versions (4.14 and 4.15) will remain unchanged in their support policy, i.e. they stay on RHEL 9.2 or 9.3
3. Support upgrade from supported previous combinations to current one. That is: 4.15+9.3 -> 4.16+9.4 and 4.15+9.2 -> 4.16 / 9.4 
4. Note: with the 9.3 special case (supported by multiple version), we had to also support step wise upgrades (e.g. first from 9.2 to 9.3, then from 4.14 to 4.15). This is explicitly out of scope. Only a direct and simultaneous upgrade of BOTH  MicroShift and RHEL is supported. This needs to be especially highlighted in the upgrade documentation, because there is a danger on rpm based systems to just do a `dnf update`, which would give you an upgrade to RHEL 9.4, bot NOT MicroShift 4.16, as this requires to manually change to the OCP 4.16 rpm repos.
5. If technically possible, it would be good to protect users against this, e.g. by adding suitable dependency to V4.15 rpms that would block an update to RHEL 9.4. 

Out of Scope

• Support for older RHEL version 9.3 and 9.2 with V4.16
• Stepwise upgrade. E.g. upgrade first to 4.16 on RHEL 9.2, then upgrade to RHEL 9.4. The first step would result in an unsupported config (4.16 on RHEL 9.2) and is not supported.

Background

"RHEL-evant" milestones for 4.16/9.4, here they are  linked to product pages:

• OCP 4.16 Engineering Candidate with 9.4 content based on CentOS Stream 9 (goal) on January 12th
• RHEL 9.4 Beta starts March 26th
  • Note that public access to beta ISO / repos starts on this date at "Remove CDN blocklist for Beta Repos"
  • Public access is required for CI to work normally, unless we replicate internal beta ISO / repos in cloud (not recommended)
• OCP 4.16 Engineering Candidate based on 9.4 Beta content (goal) on April 5th
• RHEL 9.4 GA May 7th
• OCP weekly Release Candidate builds from May 10 onwards are based on RHEL 9.4 GA (goal) weekly RCs after May 10th

MicroShift & RHEL Combinations Support Policy Considerations

Customer Considerations

Documentation Considerations

Release compatibility matrix and installation instructions need to be updated.

Interoperability Considerations

• RHEL V9.4. Verified is: RHEL supports direct 9.2 -> 9.4 upgrades
• FIPS status of RHEL 9.4 - yet unclear

Open Questions

• There might be a possibility that we can support EUS->EUS upgrades, i.e. from V4.14 directly to V4.16. That would complicate the possible upgrade paths. This needs to be investigated a bit.