`Timeout` and `TaskSpec` supported in `Custom Tasks`
`Timeout` and `TaskSpec` supported in `Custom Tasks`

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

`Timeouts`:
- TEP: https://github.com/tektoncd/community/pull/433
- PR: https://github.com/tektoncd/pipeline/pull/3976

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

This item cleans up the todo items in `RunSpec`.
tektoncd/pipeline,tektoncd/pipeline