feat: enable SSH/terminal access to Computing Units

[bobbai00]

What changes were proposed in this PR?

This PR implements SSH-like terminal access to Computing Units by integrating ttyd (terminal over HTTP/WebSocket) into the computing unit infrastructure.

• Add web-based terminal access to Computing Units using ttyd
• Users can now open a shell interface to their CUs through the web UI

Here is a simple demo:

The solution uses ttyd which provides a terminal over HTTP/WebSocket:

• Terminal runs inside each computing unit master pod
• Accessed via /wsapi/cu-ssh endpoint with authentication
• Envoy proxy handles routing based on computing unit ID
• WebSocket connection maintained for real-time terminal interaction

Terminal Access Flow:

1. User clicks "Open Terminal" for a specific CU in the UI
2. Frontend generates terminal URL with uid, cuid, and JWT token
3. Request goes through Envoy proxy to /wsapi/cu-ssh
4. Envoy routes to the appropriate CU pod on port 7681
5. ttyd serves terminal interface over WebSocket
6. User can execute commands in the CU environment

Any related issues, documentation, discussions?

Closes #3935

How was this PR tested?

Was this PR authored or co-authored using generative AI tooling?

No

[chenlica]

Adding @kunwp1 to the reviewer list.