Add mutation to create container virtual registry upstream

Overview:

• createContainerVirtualRegistryUpstream: Create a new upstream
• Support for all required and optional fields
• Proper validation and error handling

Data Model

A container virtual registry upstream contains:

• Name
• URL
• Cache expiration period (in hours)
• Optional username
• Optional password
• Association with a virtual registry (via virtual registry ID)

Check the model attributes when picking this up :) Take a look at MavenUpstreamCreateMutation.

Maven reference: !194371 (merged)