Adds Env to TaskRunSpec

[poy]

Changes

Adds a Env field to TaskRunSpec to allow a user to set environment
variables on each step container. This mimics Knative-Build's
TemplateInstantiationSpec's Env field.

Setting environment variables is useful for when a TaskRun author may
not know what variables are required ahead of time (e.g., Buildpacks).

fixes #1606

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[tekton-robot]

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[tekton-robot]

Hi @poy. Thanks for your PR.

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[imjasonh]

/ok-to-test
/hold
(For 0.10)

I need to think about how this interacts with task.spec.stepTemplate. Probably the TaskRun should win any conflicts.

[imjasonh]

/assign

[poy]

@imjasonh I followed the existing pattern established with implicitEnvVars hoping to do just that 😁

[bobcatfish]

Thanks for the contribution @poy! Before we merge this, we should discuss the design and make sure we want to add this - as mentioned in #1606 (comment) this is something we have deliberately not added support for in the past, so I'd like to dig a bit more into the use case you described in #1606 (comment) so we can understand it a bit better before merging.

/hold

[cccfeng]

Hi everyone, it's nice to see some discussions and code changes on supporting dynamic environment variables. I would like to ask how can users support dynamic env through pipelineRun?

[poy]

Hey @cccfeng, I would recommend you join the discussion in #1606

[bobcatfish]

I'm assuming we can close this for now and continue the discussion in #1606 but plz reopen if I'm wrong @poy!