[1.17] docs: add docs for conversation model info in metadata api

[sicoyle]

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Description

Dapr Agents uses the metadata api to capture information for the Agent registry. Part of this information includes the model associated with a conversation compoennt that gets registered within the Dapr runtime. This PR is the docs supporting the Metadata API addition of conversation compoennts denoting their associated model.

I'm updating only the Metadata API page here https://docs.dapr.io/reference/api/metadata_api/

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