Update JS agents code + enhance output formatting

[DanWahlin]

This pull request introduces significant updates to the quickstart.js file in the Azure AI sample project. The changes include enhancements to the agent creation and execution process, the addition of a file search agent, and improvements to logging and message handling. Key updates are summarized below.

Enhancements to agent functionality:

• Renamed runAgent to runAgents and added detailed logging for agent execution, including user prompts, run statuses, and token usage. Enhanced the agent interaction flow with a helper function (printAssistantMessage) to format assistant responses. [1] [2]

Addition of file search agent:

• Introduced functionality to upload a file, create a vector store, and use a file search tool to retrieve information from uploaded files. Added detailed logging for file uploads, vector store details, and assistant responses.

Code improvements:

• Added imports for fs, path, and fileURLToPath to handle file operations and paths. Defined __dirname for compatibility with ES modules.
• Commented out the chatCompletion function call and updated the runAgents function call to reflect the new functionality.

Error handling and event streaming:

• Implemented event-based handling for file search runs, processing events such as ThreadRunCreated, ThreadMessageDelta, and ErrorEvent. This ensures robust handling of streaming responses and errors.