interactive -p: add new `--auto-advance` flag

interactive -p: add new `--auto-advance` flag

When using the interactive add, reset, stash or checkout machinery,
we do not have the option of reworking with a file when selecting
hunks, because the session automatically advances to the next file
or ends if we have just one file.

Introduce the flag `--auto-advance` which auto advances by default,
when interactively selecting patches with the '--patch' option.
However, the `--no-auto-advance` option does not auto advance, thereby
allowing users the option to rework with files.

Signed-off-by: Abraham Samuel Adekunle <abrahamadekunle50@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>