Merge branch 'jnutt/link-to-principles-doc' into 'master'

Add importer design link to development guidelines

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/149966



Merged-by: George Koltsov <gkoltsov@gitlab.com>
Approved-by: George Koltsov <gkoltsov@gitlab.com>
Co-authored-by: James Nutt <jnutt@gitlab.com>