ref-filter: support different email formats

ref-filter: support different email formats

Currently, ref-filter only supports printing email with angle brackets.

Let's add support for two more email options.
- trim : for email without angle brackets.
- localpart : for the part before the @ sign out of trimmed email

Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Mentored-by: Heba Waly <heba.waly@gmail.com>
Signed-off-by: Hariom Verma <hariom18599@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>