rename either the "Image" type or its "image" spec property

[markfisher]

https://github.com/pivotal/build-service-system/blob/7ce7c912f99f160c548e86c25ea89892e27ab0e2/pkg/apis/build/v1alpha1/image_types.go#L39

If "image" is only one part of the type (e.g. "source" and "builder" being others), then it seems like the type should have a name that captures its breadth. Most users will probably consider "image" to be an atomic, immutable thing that sits in a registry as opposed to the name of the configuration for building multiple revisions of actual images. I don't have any particular suggestion for the latter, but the fact that the generated "Build" instances would be stamped out from this does imply that it could have "Build" in its name. Alternatively, the current Build type could be renamed to reflect it being a single execution/instance allowing this to be called "Build" instead. If I understand correctly, it would after all be the primary top-level type with which users of the "Build Service" interact.

[scothis]

I'd suggest renaming the CRD to Plan as it defines the archetype for multiple related builds including the input source and builder, and output image repository.

[markfisher]

I like that suggestion, especially as it's not a compound word.

[matthewmcnew]

#63 renames image to tag.

This mirrors the terminology that uses tag to reference a fully qualified tag.
docker build -t gcr.io/name
or
docker tag local-image gcr.io/image