Removing Conversation(Async)Client , rename listConversations -> listAgentConversations and adjusted samples

[jpalvarezl]

This pull request adds new APIs for listing conversations associated with agents, improves documentation, and updates code structure and linting suppressions. The main focus is to provide convenient methods for retrieving conversations directly from the main AgentsClient and AgentsAsyncClient classes, consolidating functionality and simplifying usage.

Key changes include:

New Conversation Listing APIs

• Added new methods to both AgentsClient and AgentsAsyncClient for listing agent conversations, supporting filtering, pagination, and returning strongly-typed Conversation objects. These methods allow users to retrieve all conversations or filter them by agent name, agent ID, order, and pagination parameters. (sdk/ai/azure-ai-agents/src/main/java/com/azure/ai/agents/AgentsClient.java, sdk/ai/azure-ai-agents/src/main/java/com/azure/ai/agents/AgentsAsyncClient.java) [1] [2]

Dependency and Import Adjustments

• Added imports for the Conversation model in both client classes to support the new APIs. (sdk/ai/azure-ai-agents/src/main/java/com/azure/ai/agents/AgentsClient.java, sdk/ai/azure-ai-agents/src/main/java/com/azure/ai/agents/AgentsAsyncClient.java) [1] [2]

Documentation Updates

• Updated the README.md to reflect the new, simplified way to create conversations and add messages, removing references to the now-removed ConversationsClient and streamlining usage examples. (sdk/ai/azure-ai-agents/README.md)

Codebase Simplification

• Removed the ConversationsClient and ConversationsAsyncClient from the AgentsClientBuilder and associated build methods, consolidating conversation management into the main agent clients. (sdk/ai/azure-ai-agents/src/main/java/com/azure/ai/agents/AgentsClientBuilder.java) [1] [2]

Linting and Suppression Updates

• Updated the checkstyle suppressions to remove entries for the deleted conversation client classes and add suppressions for the main agent client classes as needed. (sdk/ai/azure-ai-agents/checkstyle-suppressions.xml)