Add TerminationMessagePolicy in container conversion

[lbernick]

Changes

The "TerminationMessagePolicy" field for v1beta1 Step, StepTemplate,
and Sidecar, and v1 Sidecar, should be used when converting to and from
the Kubernetes container struct. They were omitted by accident, and
this commit adds them in.

/kind bug

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Release Notes

[Bug fix] Apply the TerminationMessagePolicy field for container types

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-pipeline-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/apis/pipeline/v1/container_types.go	29.8%	29.2%	-0.6
pkg/apis/pipeline/v1beta1/container_types.go	34.8%	34.8%	-0.1

[lbernick]

integration tests failed on TestPipelineRunTimeout (known flake)
unit tests failed w/ TestRealRunnerStdoutAndStderr (known flake)

/retest

[dibyom]

/test check-pr-has-kind-label

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[abayer]

/approve

[vdemeester]

/lgtm
Do we need to backport this ?

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: abayer, vdemeester

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[lbernick]

Do we need to backport this ?

Maybe? This bug causes the TerminationMessagePolicy to not work but I'm not sure anyone is actually using this. Better safe than sorry I guess?