treewide: Add missing PKG_MAINTAINER

treewide: Add missing PKG_MAINTAINER

Daniel F. Dickinson changed email address to <dfdpublic@wildtechgarden.ca>

luci-all-lxl has a maintainer Petar Koretic <petar.koretic@sartura.hr> but there is no corresponding GitHub account.
So Dirk Brenken was added as a second maintainer: he answered on an issue of the app.

When maintainer wasn't set the initial author was used, or most contributor or Jo-Philipp Wich as a default.

Signed-off-by: Sergey Ponomarev <stokito@gmail.com>