New list admin

Hi,

As per the discussion last October
(https://lists.gnu.org/archive/html/lilypond-user/2022-10/msg00047.html)
I have been made an admin for the lilypond-user, lilypond-devel
and bug-lilypond mailing lists. (If you're wondering, there was
some delay on the GNU side).

I don't view this as holding some kind of authority, but just
being responsible for some administrivia, namely rejecting spam and
accepting the rest, and providing assistance in case people need
help with using the list.

I have updated the list info pages such as
https://lists.gnu.org/mailman/listinfo/lilypond-user
to include some useful information and make the
subscription options easier to find. (The new style
was borrowed from the lilypond-user-fr list info page,
originally written by Valentin Villenave, thank
you Valentin.)

I have also removed the footer that got inserted
at the bottom of each post on bug-lilypond, because
neither lilypond-user nor lilypond-devel do this, and
as someone noted some time ago, it breaks DKIM signatures.

In order to increase the bus factor, I would like to
nominate one or two other regulars as admins. If you
feel like it, please let me know.

Best,
Jean