[PIP] Pipelines In Pipelines

[jerop]

Changes

This is an experimental project to provide support for Pipelines in
Pipelines to improve the composability and reusability of Tekton Pipelines.
The functionality is provided by a controller that implements the
Custom Task interface.

Its use cases include enabling defining and executing a set of Tasks
as a complete unit of execution and decoupling Pipeline branches
failures such that a Task failure in one branch does not stop
execution of unrelated Pipeline branches.

Pipelines in Pipelines is proposed in tektoncd/community#330
Issue is further described in tektoncd/pipeline#2134

Future work includes enabling passing in inputs through Parameters,
producing outputs through Results, propagating timeouts, among others.

/kind feature

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes docs (if user facing)
• Commit messages follow commit message best practices
• Commit messages includes a project tag in the subject - e.g. [OCI], [hub], [results], [task-loops]

See the contribution guide for more details.

/cc @afrittoli @bobcatfish @imjasonh

[afrittoli]

Thanks for this 🎉 🙏
It looks great, I added a couple of NITs / questions / comments, but nothing that cannot be addressed in a different patch.
/approve

[tekton-robot]

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[afrittoli]

Perhaps we could merge #706 first so we could see the tests running?

[afrittoli]

Thanks for all the updates @jerop .
I don't see the changes from #706 in here?
Thank you 🙏

[jerop]

Thanks for all the updates @jerop .
I don't see the changes from #706 in here?
Thank you 🙏

just pushed it, thanks :)

[afrittoli]

Thanks for all the updates @jerop .
I don't see the changes from #706 in here?
Thank you 🙏

just pushed it, thanks :)

Thank you!
Unit tests are running for PIP now, it looks like there is a failure.

[jerop]

Unit tests are running for PIP now, it looks like there is a failure.

yes, needed to add the event from the permanent error I added, fixed now

thanks for the reviews @afrittoli!

[afrittoli]

/lgtm