feat: wrap langchain.ChatAnthropic in a custom class

What does this merge request do and why?

This MR wraps the existing langchain_anthropic.ChatAnthropic in a custom class so that we can pass the Anthropic client as an input parameter.

P.S.: Langchain doesn't provide the ability to set up custom clients with every model copy. This makes it difficult to update specific model parameters for individual agents.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.