[feat] Add support for passing metadata when using integrations

[CalebCourier]

Description A user needs to be able to pass metadata to a guard call regardless of how they're interacting with it. This includes:

• Langchain
• OpenAI Proxy endpoint
• Guardrails Proxy endpoints

Why is this needed Some validators require specific pieces of metadata to run. For example, ProvenanceEmbeddings requires sources.

Implementation details The implementation will likely change based on the integration. i.e. The langchain integration can be used both client and server side, whereas the proxy use cases are server only.

End result User can pass metadata regardless of how they are interacting with Guardrails.