Describe the bug
aichat does not set the User-Agent header in its requests.

Expected behavior
Aichat should set the User-Agent header in its request. This allows for the identification and tracking of requests made by it, making it easier to diagnose and debug potential issues.

For cases where aichat is used by other tools, making the User-Agent header configurable would be beneficial, as it would enable these tools to provide additional context about the origin of the requests.

Environment

• os version: Ubuntu 20.04
• aichat version: 0.23.0