start: Reorganize into Trails (Candidate #1, Take #2)

[iesahin]

Due to branching error in #3442, I renewed the PR.

This PR updates the whole Get Started section into a "trail format" we discussed in #2496. It's an example to present the GS section into a less scary way.

[shcheklein]

Let's first keep even simpler - two trails, no need to change any content (split into separate section - it looks a bit strange). We can iterate after that if needed.

[jorgeorpinel]

Yeah, it was interesting to see all the small pages, but I don't think our engine is currently very conducive to using such short one-pagers -- maybe if we had a better <PREVIOUS, NEXT> navigation UI.

Also it's very hard to review the PR with so many file changes so for a quick proposal just 2 or 3 pages with the existing content in a different order would be better indeed.

I realize it will be pretty long for just 2 trails but let's try it (we can call it candidate #2) and take it from there.

p.s. there's a problem in the formatting of the GS index page.

[jorgeorpinel]

it's very hard to review the PR with so many file changes

I guess we can review the deployment. As for the order of sections (focusing on left-side nav), here's my general feedback:

• A bit too granular, some of these pages can be a single section e.g. Adding Files + Making Changes; or Storing & sharing + Retrieving; or all the import-related ones -- I.e. it's OK to remove some headings if you're making small changes (but no need to do so at first).
• I like the more practical renaming of some of the nav titles 👍🏼
• I'm surprised there's no overlap between trails (no repeated sections). I guess that's good?

But also, let's finish #3050 first! So it can be included in this.

[iesahin]

Closing in favor of #3455