update to tekton 0.16 for next release

[Tomcli]

/kind feature

Description:
Tekton 0.16 introduced several features that can unblock some of our older issues

• more context variables such as pipeline uid (unblock Map Argo variables to Tekton varaibles. #78)
• TaskSpec metadata, useful for distinguish task generated by kfp vs tfx
• variable substitution works on configmap and secrets
• WhenExpressions (new beta api for conditional)

Deprecation note:

• conditional v1alpha1 is deprecated
• PipelineRun.Spec.ServiceAccountNames is being deprecated in favor of PipelineRun.Spec.TaskRunSpec[].ServiceAccountName

Additional information:
[Miscellaneous information that will assist in solving the issue.]

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[Tomcli]

/assign

[Tomcli]

This will be targeted for the next major kfp-tekton release (1.x)

[Tomcli]

As I try to update to Tekton 0.16 along with the tekton go client, I discovered we might lose few backward compatibility on tekton 0.14.3 since there are some taskspec changes.

So I suggest we should create a new branch for the tekton 0.16 work first. Once Openshift pipeline supports tekton 0.16 on Openshift, then we can merge the new Tekton 0.16 changes such as the client, deployment, beta condition, etc.