feature: implement PinP reconciliation and tests

[TEP-0056]: Third PR of Pipelines-in-Pipelines feature implementation.

Child `PipelineRuns` (PinP) are created by the `PipelineRun` reconciler,
equal to the `TaskRun/CustomRun` implementations.

An event handler for child `PipelineRuns` is registered in controller
entrypoint. This will trigger the reconciliation loop when child
`PipelineRuns` change their state.

Extend `resolvePipelineState` with getter for child `PipelineRuns` using
lister and extend `runNextSchedulableTask` with a condition check for a
`PipelineTask` which is a `Pipeline` and implement the creation of
a new `PipelineRun` from the resolved pipeline state and pipeline facts.

Setting the `ChildReferences` was extended for child `PipelineRuns`.

Rename label/annotation factory.

The unit/e2e test framework was refactored and extended to prepare for
future tests. The test setup is a parent pipeline with one or more
embedded child/grandchild pipelines using the `PipelineSpec` (alpha)
field. It follows the given-when-then test flow arrangement.

The pipeline manifests yaml definitions use variables for every field
which is validated. Multiple helper functions were created equal to
reconciliation unit tests for TaskRuns/CustomRuns.

Test data factory functions were put in the `testing` package in the
`factory.go` file.

The unit tests validates:
- the status and condition of the parent PipelineRuns which should
trigger the creation of the child PipelineRuns,
- the actual created child/grandchild PipelineRuns if they have the correct
metadata i.e. name, owner reference, etc. and the embedded pipelines
from the `PipelineSpec` fields in the pipeline tasks of the parent
pipeline.

Similar checks are performed in `TestReconcile` for `TaskRun` and in
`TestReconcile_V1Beta1CustomTask` for `CustomTasks`.

The e2e tests validate:
- parent PipelineRun creation,
- child PipelineRun creation,
- successful finish of all resources,
- correct label and annotation propagation,
- amount of events published.

Similar checks are performed in
`TestPipelineRun|TestPipelineRunStatusSpec|...` for `TaskRun` and in
`TestCustomTask` for `CustomTask`.

Issues #8760, #7166.

Signed-off-by: Stanislav Jakuschevskij <stas@two-giants.com>

Author: twoGiants

pkg/reconciler/pipelinerun/controller.go

@@ -116,6 +116,13 @@ func NewController(opts *pipeline.Options, clock clock.PassiveClock) func(contex
 			logging.FromContext(ctx).Panicf("Couldn't register PipelineRun informer event handler: %w", err)
 		}
 
+		if _, err := pipelineRunInformer.Informer().AddEventHandler(cache.FilteringResourceEventHandler{
+			FilterFunc: controller.FilterController(&v1.PipelineRun{}),
+			Handler:    controller.HandleAll(impl.EnqueueControllerOf),
+		}); err != nil {
+			logging.FromContext(ctx).Panicf("Couldn't register PipelineRun informer event handler: %w", err)
+		}
+
 		if _, err := taskRunInformer.Informer().AddEventHandler(cache.FilteringResourceEventHandler{
 			FilterFunc: controller.FilterController(&v1.PipelineRun{}),
 			Handler:    controller.HandleAll(impl.EnqueueControllerOf),