Timeout and TaskSpec supported in Custom Tasks

We already designed and implemented support for 
`Timeouts` and `TaskSpec` in `Custom Tasks`. 

`Timeouts`:
- TEP: tektoncd/community#433
- PR: #3976

`TaskSpec`:
- TEP: https://github.com/tektoncd/community/blob/main/teps/0061-allow-custom-task-to-be-embedded-in-pipeline.md
- PR: #3901

This item cleans up the todo items in `RunSpec`.

pkg/apis/pipeline/v1alpha1/run_types.go

@@ -78,10 +78,6 @@ type RunSpec struct {
 	// Workspaces is a list of WorkspaceBindings from volumes to workspaces.
 	// +optional
 	Workspaces []v1beta1.WorkspaceBinding `json:"workspaces,omitempty"`
-
-	// TODO(https://github.com/tektoncd/community/pull/128)
-	// - timeout
-	// - inline task spec
 }
 
 // RunSpecStatus defines the taskrun spec status the user can provide