And separates the existing Gerrit provider to a new GoogleSource one.

Closes #1953

This reverts commit 2db3ae4378.

Honors `git.repositoryScanMaxDepth` if not overridden

Refs: #1869

Refs: #1886

Adds better log out support

Adds a "system" option to follow the system locale

Trying to improve clarity that there are only a small subset of features that require an account

Removes GK auth extension dependency

Adds a limit on the number of queries

- adds headings, and moves the majority of text content to the body of each step
- most steps now have a simple, one-line description
- adds "try now" section to premium feature walkthrough with a button to try
- adds and updates content in premium feature introduction step
- removes an unnecessary file

Aligns with other gate messaging states
  Simplifies context keys for premium
Fixes purchase link to point to account site
Polishes other gate messaging

Reduces startup impact