Pipeline: Reserve "tekton/" folder in taskrun filesystem

[dibyom]

We should consider reserving the tekton/ folder in the taskrun filesystem and perhaps even move stuff from the current builder/ folder to tekton/.
The tekton folder could contain internal tools as well as things like the proposed JSON file containing the pipelinerun context and any other filesystem based standards we add in the future

@ahpook pointed out that Github actions does something similar by reserving the /github folder i.e. the /github/workflow/event.json contains the request payload.

[bobcatfish]

I really like this idea!!

(related: #1030 )

[ImJasonH]

+1000

We could validate that requested TaskRuns don't request any volumeMounts over that path.

[vdemeester]

I thought I commented on this issues but I only added reactions :stuck_out_tongue:
I am also +:100: on this idea ! And validating it on the TaskRun too

[abayer]

+1 from me!

[bobcatfish]

+1 from me but might want to do some of this across 2 releases (i.e. support /tekton and /builder for some things if possible?) b/c of features such as https://github.com/tektoncd/pipeline/blob/master/docs/resources.md#surfacing-the-image-digest-built-in-a-task and as @ImJasonH pointed out, many examples using /builder

But also not totally opposed to just going for it, as pointed out in #1030 (which i think this will basically fix!!) this isn't in our api compatibility policy anyway

[vdemeester]

First step is #1440
@dibyom @ImJasonH should I assign one of you on this one ? :stuck_out_tongue:

[bobcatfish]

Update from @dibyom : @ImJasonH is waiting to finish his refactoring of pod logic before merging this one