Merge branch 'ab/dedup-config-and-command-docs'

Merge branch 'ab/dedup-config-and-command-docs'

Share the text used to explain configuration variables used by "git
<subcmd>" in "git help <subcmd>" with the text from "git help config".

* ab/dedup-config-and-command-docs:
  docs: add CONFIGURATION sections that fuzzy map to built-ins
  docs: add CONFIGURATION sections that map to a built-in
  log docs: de-duplicate configuration sections
  difftool docs: de-duplicate configuration sections
  notes docs: de-duplicate and combine configuration sections
  apply docs: de-duplicate configuration sections
  send-email docs: de-duplicate configuration sections
  grep docs: de-duplicate configuration sections
  docs: add and use include template for config/* includes