Improve onboarding experience

Created by: attfarhan

Stub issue for improving the site admin and user onboarding experience in 3.14.

• Create RFC to:
  • provide background on problems with the current onboarding experience
  • list and link current open issues related to onboarding
  • propose potential solutions to problems
• Immediate improvements to the onboarding checklist

Issues:

• https://github.com/sourcegraph/sourcegraph/issues?q=is%3Aopen+is%3Aissue+label%3Aonboarding
• https://github.com/sourcegraph/sourcegraph/issues?q=is%3Aopen+is%3Aissue+label%3Aonboarding-test-1