[3.12] Docs: Argument Clinic: Restructure "Basic concepts and usage" (GH-106981)...

[3.12] Docs: Argument Clinic: Restructure "Basic concepts and usage" (GH-106981) (#107325)

Split "Basic concepts and usage" into:

- Reference
  - Terminology
  - CLI reference

- Background
  - Basic concepts

(cherry picked from commit 2ad699002e3ce09e9fa41e333ac72f16a32d94de)

Co-authored-by: Erlend E. Aasland <erlend@python.org>
Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com>