[ELPA] New package: marginalia

[Daniel Mendler]

We want to submit the package "marginalia" to GNU ELPA. The package
enhances existing commands with completion categories and
`annotation/affixation-functions` for rich annotations.

Marginalia works with the default *Completions* UI, Vertico (GNU ELPA),
Selectrum (MELPA) and Icomplete-vertical (MELPA). Ivy (GNU ELPA) support
is in the works; there is an open PR
(https://github.com/abo-abo/swiper/pull/2875).

The Marginalia source and a README can be found at
https://github.com/minad/marginalia.

Thank you!

Daniel Mendler
(co-maintainer with Omar Antolín Camarena)