feat(cli): add exit tips for conn

[ysfscream]

PR Checklist

If you have any questions, you can refer to the Contributing Guide

What is the current behavior?

When users successfully establish a connection using the mqttx conn command, the program maintains the connection state (appearing to be "hanging"). Still, there is no prompt for users to exit. This causes users to need clarification about the program's behavior.

• Users are unclear that the expected behavior of the mqttx conn command is to maintain the connection
• Users don't know how to exit the connection state properly
• Lack of user guidance leads to poor operational experience

Please describe the current behavior and link to a relevant issue.

Issue Number

Example: #1810

What is the new behavior?

❯ mqttx conn
✔ Connected
- Press Ctrl+C to disconnect and exit

Please describe the new behavior or provide screenshots.

Does this PR introduce a breaking change?

• Yes
• No

Specific Instructions

Are there any specific instructions or things that should be known prior to review?

Other information