feat(api): update proto for collections of Pipelineparameter channels

[zazulam]

Description of your changes:
This is a pre-requisite PR needed for additional changes to pass CI for #11219 to help resolve #10840.

I have validated these changes from a local build of the apiserver image that references this pipelinespec rather than the go import from github.

Checklist:

• You have signed off your commits
• The title for your pull request (PR) should follow our title convention. Learn more about the pull request title convention used in this repository.

[google-oss-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[google-oss-prow]

Hi @zazulam. Thanks for your PR.

I'm waiting for a kubeflow member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[zazulam]

cc: @chensun @HumairAK @hbelmiro

[chensun]

Non-trivial API changes should always start with a design and get consensus from the community first: https://github.com/kubeflow/pipelines/blob/master/CONTRIBUTING.md#contribution-guidelines

For this specific change, see my comment in #10840 (comment)

/hold