feat(api): Add SemaphoreKey and MutexName fields to proto

[DharmitD]

Description of your changes:
This PR introduces semaphoreKey and mutexName fields in PipelineConfig proto to support pipeline-level concurrency controls in KFP.
Pre-requisite to #11340

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[google-oss-prow]

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[VaniHaripriya]

/lgtm

[rimolive]

/lgtm

[HumairAK]

/ok-to-test

[github-actions]

Approvals successfully granted for pending runs.

[gregsheremeta]

lgtm but waiting for #11370

/hold