Add wait_for_participant to mma example

[bcherry]

This was already in other VPA examples but missing here. It's not always necessary but improves reliability (e.g. SIP) and seems worth having in the default case.

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[theomonnom]

Hey for VPA it is already handled internally. I think we should do the same for MMA

[theomonnom]

It is already the case actually: https://github.com/livekit/agents/blob/5fedcfdfce510ce96d34d85b38807f0d03389bfc/livekit-agents/livekit/agents/multimodal/multimodal_agent.py#L232

[bcherry]

@theomonnom yeah but still all the VPA examples have a wfp in them - is it really unnecessary?

this could be indicative of some sort of bug with how it's set up - it does seem like that should basically work (although it doesn't wait for subscription from the linked_participant but rather from any participant). and someone in community reported that SIP didn't work til they added this. might be worth digging into, I agree it feels unnecessary and it would be good to simplify it away in all of the examples.

[theomonnom]

Seems like wait_for_participant was already added by dz in some previous PRs (inside the example/multimodal_agent)