Backport [MS3] Better Onboarding: "Add Data" discoverability (#49813)

* Re-introduce "Upload CSV" button for instances with DWH attached (#49545)

* Move the upload CSV button to the main nav bar

* Remove the old `SidebarOnboardingSection`

* Remove obsolete unit tests

* Rework E2E tests

* Add some spacing around the button

* Fix E2E test

* Break `MainNavbar` unit test down

* Expand unit tests

* Update E2E tests

* Fix E2E test failure

* Move JSDoc where it belongs

* Provide context for translators

* Simplify the condition

* Make "Add database" more prominent (#49678)

* Remove dead code from browse models page

* Use the grid to control the gap

* Implement "Add database" button

* Add basic unit tests

* Make sure the feature works when there are no databases

* Add analytics to the db list

* Add "Add database" button to the sidebar

* Add E2E Snowplow tests

* Add unit tests

* Deal with authentication in each beforeEeach separately

* Add Snowplow E2E test for a database card

* Slightly tweak the title line height