feat: autostart custom notebook (#1781)

[andre-code]

PR to include the path to the notebook file in the modal to share the session link.

How it works

Closes #1781

/deploy #persist

[RenkuBot]

You can access the deployment of this PR at https://renku-ci-ui-1905.dev.renku.ch

[ciyer]

While adding this feature, could you fix this rendering problem?

[ciyer]

This is very useful!

After discussions, I have some requests to make a few changes.

1. The link should be available for any file in the project, not just notebooks
2. For the case that the user does not want to specify the branch/commit, I think a simpler UX where the pop-up appears over the file browser would be better.

Only if the user asks to specify the branch/commit should they get redirected to the "Start notebook" page.

3. Let us say which file you will return to if you do get redirected to the "Start notebook" page.

[ciyer]

This feature should be available for any file, not just notebooks.

[andre-code]

sure, added in the last commit

[ciyer]

I think this would be nicer as text.

Suggested change

	<FormGroup key="notebook-file-path">
	<Label><b>Notebook:</b> {notebookFilePath}</Label>
	</FormGroup>
	) : null;
	<FormGroup key="notebook-file-path">
	<Label>With <b>{notebookFilePath}</b> initially open</Label>
	</FormGroup>
	) : null;

[andre-code]

@ciyer Thanks for your review, I really like the suggestion. Please find the implementation of this in the latest commit.

[ciyer]

This works very nicely!

There are some improvements to the session start page that should be made to make this clearer, but I think it would be better to incorporate that into the broader session redesign in #1805.

Once the tests pass, I think this can be merged.

[RenkuBot]

Tearing down the temporary RenkuLab deplyoment for this PR.