Fix idle shutdown from happening when active process is still running

[NewtonDer]

Issue

Description of Changes

Problem:
If user starts a process in the Terminal and closes the browser tab, the SageMaker Code Editor space will still automatically shut down after the idle timeout.

Explanation:
The sagemaker-idle-extension's checkTerminalActivity method halts when the browser tab is closed. Thus, it is unable to detect any running processes and avoid the idle timeout.

Solution:
Moves sagemaker-idle-extension's checkTerminalActivity method to server side in webClientServer. This method is called in the /api/idle handler, which currently happens on a 1 minute interval.

Testing

Tested with a custom image deployed in a SageMaker AI Studio domain.

Screenshots/Videos

Additional Notes

This same fix is already launched and working in sagemaker-code-editor versions 1.5, 1.6, and 1.7.

Backporting

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[vpaiu]

The build fails without this line (The exact build error: Error: /home/ubuntu/environment/code-editor/code-editor-src/src/vs/server/node/webClientServer.ts(602,25): Cannot find name 'spawn'.).

I added back this line when testing for the build to be successful.

[NewtonDer]

thank you!

[vpaiu]

After I fixed locally the build error I did the following to test the idle-extension:

1. Created the sagemaker image with the build artifact.
2. Created the sagemaker code editor space in SageMaker Unified Studio with the image created.
3. Tested that the timestamp is updated properly by executing cat /tmp/.sagemaker-last-active-timestamp in the terminal in the code editor space. It printed the expected timestamp.
4. Tested that the api edpoint (/api/idle/) was returning the correct timestamp. I did this by executing fetch(window.location.pathname + '/api/idle').then(r => r.json()).then(console.log) in the web developer tools console. It returned the correct timestamp.