Replace content outlines with well-chosen first-level titles

### Problem

The docs page layout renders the top-level titles of a page in the right side-bar, which is shown automatically on a wide screen. This makes the content outline redundant. See the screenshot below. Moreover, no docs other than the QS docs use such content outlines.


### Proposal

- Drop content outlines from all quickstart docs
- Double-check that the right-sidebar titles provide fine-grained enough navigation; and fix missing navigation structure by
- adding additional top-level section titles or
- splitting content into a sub-page that gets indexed in the left-side ToC (for large pieces of content).

FYI: @hrischuk-da @miller-da @filmackay-da @andrae-da

Start by reviewing all quickstart docs that use content outlines, then compare their top-level titles with the automatically shown right sidebar and the left-side table of contents. Done means content outlines are removed, each page has sufficiently fine-grained navigation, and large sections are split into indexed sub-pages where needed.

Written by the indexing model from the issue text.