doc/dev: migrate continuous_integration.md to ci/index.md
Created by: bobheadxi
- Shorter URL - with
/background-information
being as long as it is, tackingcontinuous_integration
on the end of that is unweidly - Directory for us to split out the currently very large continuous integration page into multiple pages
Test plan
sg lint docsite
Also validated the redirect works, including with anchor links, on sg run docsite