Docs: Refactor "Importing your documentation"

[benjaoming]

Currently, Importing your documentation is nested in the Tutorials section.

But it's not really a tutorial.

The current content will mislead a user looking for an easy tutorial. For the fast reader, the page might also wrongly convey only the manual method since the automatic method is easy to miss.

I would propose:

1. Create a how-to from the manual parts: "How to import a Git repository manually" ✔️
2. Create a feature reference about Automatic Import of Git repositories ✔️
3. Update the current Getting Started tutorial with references to these.
4. Redirect the old page to the new feature reference

[benjaoming]

Update: The first 2 items are now satisfied by new pages that were added recently so this should be much easier to implement.

[humitos]

This seems done already. We are linking to the manual import guide from getting started now.