Conditionals: Add Condition CRD and API changes to pipelines to add conditions

[dibyom]

Tracking issue for API changes for conditional execution + initial implementation based on the design in #27

ref: #1137

[objectiveous]

I left a comment here but I'm not sure if you'd see it.

Please consider a "break pointing" condition. For example, imagine you have a GUI w/ an Operations view of running Tekton Pipelines and you discover a PipelineRun that is failing. You might want to rerun the pipeline but pause execution at the beginning of a Task in order to exec into the Pod to inspect the environment.

Does this make sense to model as a Condition?

[dibyom]

Hi @objectiveous ! Interesting use case. The initial implementation of conditionals won't have support for this but we do have #233 open for adding support for pausing tasks till a condition is met.

[dibyom]

/assign

[m1093782566]

I think it's really an important feature which is required in my environment.

[dibyom]

Closing this since we have added the APIs as well as an implementation that allows running condition containers, along with variable substitution support for parameters.