[3.12] GH-92584: Move installation schemes overview to sysconfig docs (GH-108018) (#110213)

GH-92584: Move installation schemes overview to sysconfig docs (GH-108018)

* Add new installation path functions subsection

* Add content from install/index to sysconfig

* Fix table

* Update note about installers

* Clean up the list of schemes, remove references to Distutils
(cherry picked from commit f16e81f368d08891e28dc1f038c1826ea80d7801)

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>