- Make all specific problems H2-level headings.
- Create a `doc-toc` div at the top for the table of contents.
  - Don't use `learn-doc` because we may want to style/show this one independently.
- Link to all problem headings.

Note: can't use metadata in a page header because our CI tools splat their own headers into these pages, so anything we add becomes part of the page body.

* Outlining items for troubleshooting guide for sandboxing.

* Update docs/troubleshooting-guide/sandboxing.md

Co-authored-by: flamber <1447303+flamber@users.noreply.github.com>

* Incorporating minor suggestions

* Incorporating comment from @flamber

* Converting sandboxing troubleshooting guide to prose

* Update docs/troubleshooting-guide/sandboxing.md

Co-authored-by: flamber <1447303+flamber@users.noreply.github.com>

* Johannes' fixes

* Update docs/troubleshooting-guide/sandboxing.md

Co-authored-by: Jeff Bruemmer <jeff@metabase.com>

* Update docs/troubleshooting-guide/sandboxing.md

Co-authored-by: Jeff Bruemmer <jeff@metabase.com>

* Update docs/troubleshooting-guide/sandboxing.md

Co-authored-by: Jeff Bruemmer <jeff@metabase.com>

* Update docs/troubleshooting-guide/sandboxing.md

Co-authored-by: Jeff Bruemmer <jeff@metabase.com>

* Update docs/troubleshooting-guide/sandboxing.md

Co-authored-by: Jeff Bruemmer <jeff@metabase.com>

* Update docs/troubleshooting-guide/sandboxing.md

Co-authored-by: Jeff Bruemmer <jeff@metabase.com>

* Update docs/troubleshooting-guide/sandboxing.md

Co-authored-by: Jeff Bruemmer <jeff@metabase.com>

* Update docs/troubleshooting-guide/sandboxing.md

Co-authored-by: Jeff Bruemmer <jeff@metabase.com>

* Jeff's edits

Co-authored-by: flamber <1447303+flamber@users.noreply.github.com>
Co-authored-by: Jeff Bruemmer <jeff@metabase.com>