This commit adds the basic APIs for conditionals in Tekton:
1. Condition CRD defines a condition how a condition is evaluated i.e.
the container spec and any input parameters.
2. The `Conditions` field in `PipelineTask` references `Condition`
resources that have to pass before the task is executed.
3. The `ConditionChecks` field in `PipelineRun.Status.TaskRuns` surfaces
the status of conditions that were evaluated for that particular task.
b91640d7db