Respect `NOTMUCH_CONFIG` and `NOTMUCH_PROFILE` environment variables

[gnull]

Currently, notmuch-addrlookup-c fails to find the Notmuch config anywhere other than ~/.notmuch-config.

For example, notmuch-config(1) allows me to put my config in ~/.config/notmuch/foo/ and do:

NOTMUCH_PROFILE=foo notmuch search bar

but

NOTMUCH_PROFILE=foo notmuch-addrlookup kek

doesn't work.

Ideally, notmuch-addrlookup should support all behavior described in FILES section at the end of notmuch-config(1).