Search kit: Document how to get selected ids for non-contact search tasks

See merge request !1023

Add chapter "Service Container"

See merge request !1022

Make clearer when making form builder available to a custom entity.

See merge request !1025

remove incorrect statement that APIv4 is not available via rest...

Closes #878

See merge request !1021

remove incorrect statement that APIv4 is not available via rest (https://docs.civicrm.org/dev/en/latest/api/v4/rest already exists)

HookInterface changed namespace from Civi\Test to Civi\Core

See merge request !1020

docs: describe bootstrap in Drupal 9

See merge request !1019

Referring to https://github.com/civicrm/civicrm-drupal/pull/495

commented out "to-do" notes from financial chapter

See merge request !1012

commented out "to-do" from extensions/index.md

See merge request !1016

add icon parameter to summaryActions hook

See merge request !1018