feature: Support deserializing to OpenAPI spec v3 parameter object string

[jpmcb]

For function calling params, the Google gen AI libraries used by agent API expect an OpenAPI v3 param object:

https://github.com/google/generative-ai-go/blob/1a2951b1bd5ed24672876dd3115095ec8d00c3be/genai/internal/generativelanguage/v1beta/generativelanguage-api.json#L3594-L3597

Parameter - Optional. Describes the parameters to this function. Reflects the Open API 3.03 Parameter Object string Key: the name of the parameter. Parameter names are case sensitive. Schema Value: the Schema defining the type used for the parameter.

gsv should be able to support deserializing to both json schema and open API v3 param string