#933947 contributors: add redirection to the standard name of a user

#933947#3
Date:
2019-08-05 12:27:55 UTC
From:
To:
DDPO contains links for every email address to
contributors.d.o/contributor/{{ email }}, so for example my own DDPO
page has a link to both
https://contributors.debian.org/contributor/mattia%40debian.org/
https://contributors.debian.org/contributor/mattia%40mapreri.org/
The latter actually returns a 404, but it should IMHO redirect to the
first one.

contributors itself aims at connecting multiple identities, together
with `carnivore`, so it should already have all the required data.