gator test add support for --image for templates and constraints

[apeabody]

Describe the solution you'd like
I'd like to store my templates and constraints in a container image and use them directly with gator test.

For example to test my-manifest.yaml: cat my-manifest.yaml | gator test --image gcr.io/repo/templates-and-constraints:1.0

[maxsmythe]

We should consider being able to support multiple instances of the --image flag in the same invocation.

[sozercan]

Is this only for gator CLI and not for webhook? I think we had a separate discussion for webhook in #1491

gcr.io/repo/templates-and-constraints:1.0

how would we include constraints in there? wouldn't these have arbitrary parameters?

[apeabody]

Hi @sozercan - My initial use case would be that an end-user would "layer" their own (pre-configured if required) constraint files into a container image along with any custom constraint templates, and then publish the container image to a registry as part of their pipeline. They could then call it using gator, easily test against different version of the container, etc.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.

[apeabody]

Ref: #2398