add Install button to trigger Epinio install on unregistered clusters

[psanghvi17]

PR Checklist

• Linting Test is passing
• Code is well documented
• If applicable, a PR in the epinio/docs repository has been opened

Summary

Fixes #
Adds an Actions column to the Epinio instances table with an Install button that appears only for clusters where Epinio is not yet installed. Clicking the button opens an InstallDialog that collects domain, targetNamespace, and version, checks for an existing active install to prevent duplicates, creates an InstallEpinio CR on the target cluster via the Rancher K8s proxy, and polls the CR status conditions to show live progress (Progressing / Available / Degraded) until the operator completes the Helm-based install.

Occurred changes and/or fixed issues

• An Install button appears in that column only for clusters whose state is uninstalled (i.e. clusters registered in Rancher that do not yet have Epinio running).
• Clicking Install opens a new InstallDialog that collects the three required inputs: Domain, Target Namespace (defaults to epinio), and Version.
• On submit the dialog checks for an existing active install (Available=True or Progressing=True) for the same target namespace on the same cluster, preventing duplicate installs.
• If no duplicate is found, the dialog creates an InstallEpinio custom resource on the selected cluster via the Rancher Kubernetes API proxy (/k8s/clusters/{id}/apis/epinio.apps.example.com/...).
• After the CR is created the dialog polls its status.conditions every 4 seconds and surfaces the operator's live progress to the user. The user can close the dialog early; the install continues in the background.- A new InstallDialog component is registered in the plugin entry point so Rancher's promptModal mechanism can resolve it by name.

Technical notes summary

Areas or cases that should be tested

Areas which could experience regressions

Screenshot/Video

[dcharles525]

LGTM