Add our support matrix links to welcome

[aburdenthehand]

What happened:
Background: A question was asked in our Community Meeting this week (May 8th, 2024) about what versions of KubeVirt we support, and where the "EOL" support line is drawn (in the meeting I said that my understanding was We support the last three versions as per our support matrix and any older versions fall into the category of "if someone from the community feels personally compelled or invested to help out with the issue then they might, but it cannot be expected". When asked this distinction was documented somewhere, we couldn't find it in the meeting. But that's because we didn't look in kubevirt/kubevirt/docs/kubernetes-compatibility.md, a file that predates our support matrix and could do with a bit of an update.

I propose that we:

• update kubernetes-compatibility.md to point to our support matrix and whatever other housekeeping update is required.
• Add the relevant text (#support-extensions) to our support matrix.
• Add this info to our user-guide in docs/index.md#getting-help -> because the question of 'Is your version of k8s+kubevirt supported?' is an oft-asked first step to troubleshooting

This touches 3 repos (hooray) but it can probably be safely all tracked here. (But if someone wants to raise the appropriate bugs in those other repos then you are of course welcome.)

FYI @EdDev @orelmisan @larrydewey

[anishbista60]

@aburdenthehand Can i work on this issue or it is for Kubevirt member only ?

[aburdenthehand]

@anishbista60 sorry for the delay. You are very welcome to work on this!

[kubevirt-bot]

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