Add Optional Control for Participant Auto-Linking in PipelineAgent

[dsgolman]

This is the complimentary code PipelineAgent for the MultiModalAgent auto linking code.

The main difference is the creation of the public facing link_participant rather than exposing/using the internal private _link_participant like the multimodal was done.

Mainly pushing this so I can point to it in my production.

[changeset-bot[bot]]

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Latest commit: 4b08681369425305a916a1ca091f5c2191204807

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