e2e: Adds basic e2e test for Pipelines LTS versions.

[wlynch]

Changes

Refactors e2e test to a reusable workflow.

We should add more tests to make sure we're hitting some of the deprecated features, but this at least adds the scaffolding to make sure we're running against these versions.

Fixes #716

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Release Notes

NONE

[tekton-robot]

Skipping CI for Draft Pull Request.
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[lcarva]

/lgtm

Nice!

[tekton-robot]

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