ci-operator: add TestStep type

[bbguimaraes]

Slightly modified subset of #85.

Open questions:

• Is a step with just a name the best way to reference a pre-defined step? See the original PR for details and https://github.com/bbguimaraes/release/tree/steps for an example.
• Is resources required? That is the case for other ci-operator tests, but not for templates.
• TestStep is a terrible name.

[stevekuznetsov]

As a first pass, we should be concerned with identifying the set of information necessary to work with downstream/at runtime. Let's validate that every field exists, resources are set, etc. No concept of name resolution yet

[bbguimaraes]

Another one:

• We need a way to reference an image that is not part of the pipeline,

Container tests don't have that problem because they simply don't allow it, templates use the IMAGE_/LOCAL_IMAGE_ prefixes.

[stevekuznetsov]

As this is a string and not a PipelineImageReference don't we already allow any pull spec here?

[bbguimaraes]

There are two points in the execution where this is used:

• When configuration is loaded, to determine dependencies between (ci-operator) steps.
• When the pods are created.

The biggest problem is #1. We know at that point the images that are part of the pipeline, but not those that come from tag_specification.

For #2, we can always use pipeline:src, stable:tests, or even a full spec, which is what I've been using, but since #1 requires us to have that information, that should not be required.

[stevekuznetsov]

So we generally operate on the concept that if an image is named foo and there exists a foo in the images brought in by the tag_specification, the built image overrides that which is pulled in. So, we can accept a simple string here and:

• if it matches something that is built by the pipeline or the images, create that link in the steps
• if it does not, expect it to be provided by the import from tag-specification

[bbguimaraes]

That's what I wanted to hear/read.

[stevekuznetsov]

/lgtm

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