jx gitops image to support registry/arch modification

[jstrachan]

we should add CLI arguments to allow the registry prefix on image strings to be modified for Deployments / Jobs.

Eg

jx gitops image —from-registry gcr.io —to-registry my-registry-host

would then replace any files in content-root/**.yaml which have a container image like gcr.io/myorg/myimage => my-registry-host/myorg/myimage

also it would be nice to be able to add a —arch arm64 argument to modify the image to reference the arm64 architecture

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