Add pages for StepActions

[AlanGreene]

Changes

Resolves #3348

Add list and details pages for the v1alpha1 StepActions resources following the same pattern as the existing Tasks / Pipelines page. The only difference is that we don't link to associated runs or provide the ability to create a run as a StepAction must be used in a Task and cannot be run standalone.

/kind feature

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[AlanGreene]

/test all

[AlanGreene]

StepActions was added in Pipelines v0.54.0 and is currently alpha. It is expected to be promoted to beta around the v0.60.0 / June timeframe.

The latest Dashboard release (v0.45.0) still supports Pipelines v0.53.0, so we might wait until we drop support for that before landing this change.

[AlanGreene]

/test all

[tekton-robot]

@AlanGreene: PR needs rebase.

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