Pattern: Replicated registry proxy

[adamancini]

Capture a pattern that outlines how a vendor would configure their first-party and third-party Helm charts to use images distributed through the Replicated registry.

The pattern doc should include:

• Helm templates over the repository/registry portions of an image URL
• Values file inputs that an end user would use to install their application through the Replicated registry
• with EC, the new proxy field should be shown and demonstrated