.NET: Copy AdditionalProperties from AgentRunOptions to ChatOptions in ChatClientAgent #3179

In some cases callers may want to pass additional context to an agent and be able to access that in a function tool.

Currently, if users were to set AdditionalProperties on AgentRunOptions, and call ChatClientAgent, those additional properties are not propogated to the ChatOptions passed to the ChatClient. You have to break out of the abstraction and set a ChatOptions on ChatClientAgentRunOptions to pass any AdditionalProperties.

We should automatically pass any AdditionalProperties on AgentRunOptions to ChatOptions in ChatClientAgent, so that users don't have to break out of the abstraction to pass additional properties all the way down the stack.