Update Documention for Openhsift installation

[gizas]

As part of the continuous improvement effort for our user experience for Kubernetes Support, we identified a possible improvement on the the documentation for Red Hat Opehisft support.

In more details, we currently have a dedicated section under standalone elastic agent : https://www.elastic.co/docs/reference/fleet/running-on-kubernetes-standalone#_red_hat_openshift_configuration

This section gives the impression that we faulty support the Kubernetes integration installation for Openshift only for standalone, which is not correct. All the steps described above can also be done in the respective boxes of the Managed Elastic agent.

In more details, this issue will focus and try to:

• Propose a new landing page and structure for openshift that will clarify the steps for Managed vs Standalone installations
• Add links for the advanced-kubernetes-managed-by-fleet section of kubernetes and why a customer should use it and why. Pages like advanced-kubernetes-managed-by-fleet should belong to some additional installation scenarios where we want to meet specific user scenarios
• Update the support matrix of k8s integration and add details for all the flavours of kubernetes we test vs we support in the matrix. There might be k8s versions that we have tested in the past and we have implemented integrations for them but we can not quarantee the SLA support as their version progress. We should list specific flavours and openshift belongs to this category.

cc @eedugon , @mlunadia , @lucabelluccini