Support airgap image prefix for primehub-controller

[qrtt1]

PR checklist

• [x] Ensure you have added or ran the appropriate tests for your PR.
• [x] DCO signed

What type of PR is this?

enhancement

What this PR does / why we need it:

support air-gap image prefix for ph-controller

Which issue(s) this PR fixes:

sc-24401

Special notes for your reviewer:

1. introduce the new settings to values.yaml

 controller:
   airgap:
     imagePrefix: ""

2. the value would be overridden by PRIMEHUB_AIRGAPPED_IMAGE_PREFIX env from helmfile