Merge branch 'ma/pager-per-subcommand-action' into maint

Merge branch 'ma/pager-per-subcommand-action' into maint

The "tag.pager" configuration variable was useless for those who
actually create tag objects, as it interfered with the use of an
editor.  A new mechanism has been introduced for commands to enable
pager depending on what operation is being carried out to fix this,
and then "git tag -l" is made to run pager by default.

If this works out OK, I think there are low-hanging fruits in
other commands like "git branch" that outputs long list in one mode
while taking input in another.

* ma/pager-per-subcommand-action:
  git.c: ignore pager.* when launching builtin as dashed external
  tag: change default of `pager.tag` to "on"
  tag: respect `pager.tag` in list-mode only
  t7006: add tests for how git tag paginates
  git.c: provide setup_auto_pager()
  git.c: let builtins opt for handling `pager.foo` themselves
  builtin.h: take over documentation from api-builtin.txt