Fix home page cluster description scaling issue

[richard-cox]

Summary

Fixes #11588

Occurred changes and/or fixed issues

• mgmt cluster is a steve resource, so can inherit the steve model
  • this resolve the issue of mgmt cluster not having a description
• prv cluster uses it's own description, falls back on mgmt description
  • custom stuff on home screen not needed
  • fixes description on detail page of legacy clusters
• remove description from hybrid model
  • this contains steve references and isn't needed

Technical notes summary

home page prov.description --> prov's description from extended steve model || mgmt's description from extended steve model

Areas or cases that should be tested

• One of EKS/AKS/GKE cluster created in old ui AND RKE2 cluster description should display on
  • home page cluster list
  • side nav
  • cluster's detail page

Screenshot/Video

Checklist

• The PR is linked to an issue and the linked issue has a Milestone, or no issue is needed
• The PR has a Milestone
• The PR template has been filled out
• The PR has been self reviewed
• The PR has a reviewer assigned
• The PR has automated tests or clear instructions for manual tests and the linked issue has appropriate QA labels, or tests are not needed
  • Automated tests have been written for description in
    • https://github.com/rancher/dashboard/pull/10487/files
    • https://github.com/rancher/dashboard/pull/10782/files
• The PR has reviewed with UX and tested in light and dark mode, or there are no UX changes

[aalves08]

@richard-cox , I've created a RKE1 GKE cluster using the old UI and RKE2 Digital Ocean Cluster and I can see the descriptions in the key areas, so I would say LGTM!