Test and document procedures using the mirror-plugis.sh script with Operator-based RHDH deployments on both OpenShift and vanilla Kubernetes.

Requirements:

Initially the goal here was to create proven documentation to guide the official docs issue (RHIDP-9242) but it make sense to create new documentation file also within rhdh-operator/blob/main/docs/airgap-plugin-mirroring-operator.md

The documentation must include:

• requirements
• architecture overview
• partially Connected Environment Workflow
• Fully Disconnected Environment Workflow
• Mixed Mode: Catalog + Custom Plugins
• File-Based Plugin List
• Configuring Backstage CR
• Creating ImageDigestMirrorSet (OpenShift)
• edge cases, etc