doc: fix config API documentation about config_with_options

doc: fix config API documentation about config_with_options

In commit dc8441fdb ("config: don't implicitly use gitdir or commondir",
2017-06-14) the function git_config_with_options was renamed to
config_with_options to better reflect the fact that it does not access
the git global config or the repo config by default.

However Documentation/technical/api-config.txt still refers to the
previous name, fix that.

While at it also update the documentation about the extra parameters,
because they too changed since the initial definition.

Signed-off-by: Antonio Ospite <ao2@ao2.it>
Signed-off-by: Junio C Hamano <gitster@pobox.com>