Update my committer name and add my new mentor relationship

Regarding the name change

A few years ago I changed my legal name to "Enji Cooper". When I rejoined the
project, I requested that accounts@ use my legal name instead of my [previous]
nickname. This change syncs up a reference to use the proper name for clarity.

Regarding the new mentor relationship

@emaste and @jtl graciously accepted my request to mentor me this time around
with my src commits while I get up to speed.

I am leaving my previous mentorship details in committers-src.dot for historical
reasons, per @emaste's request.

• Thank you very much @jmmv and @rpaulo for the help with my previous mentorship; I really appreciate it!

Approved by: emaste (mentor)
Differential Revision: https://reviews.freebsd.org/D18644