[UI] Support exporting pod stdout and result

[senwang86]

Summary

• When exporting, the pod's stdout and result are written to a Jupyter notebook
• "Raw JSON" export functionality is moved to the frontend
• The Jupyter notebook result is imported in addition to the entire notebook
• Bug fix: "execution_count" is returned from runtime server now

Test

[lihebi]

Let's add date to the exported filename and keep consistent with the .ipynb export.

codepod/ui/src/components/Sidebar.tsx

Lines 891 to 893 in 554cdac

	const filename = `${
	repoName || "Untitled"
	}-${new Date().toISOString()}.ipynb`;

[lihebi]

Nevermind, I made this minor change. Merging.

[lihebi]

We should display the execution count in the output area of a Code pod. This PR already gets packed, let's implement it in another PR.

[forrestbao]

execution_count is a property of both a code cell and its output (if the output type is execute_result) #411

[lihebi]

Thanks, Sen!