Debian-Med's */d/u/metadata yamllint-clean

[Steffen Möller <steffen_moeller@gmx.de>]

Hello,

I have completed my iteration of yamllint-fixes on d/u/metadata files.
Debian Med only, admittedly. Would be something for lintian, I suppose.
This was meant as a preparation to somehow semi-auto-add references to
conda. This needs to wait a bit, now. Need a plan, first. My initial
idea was to just prepare a table and then generate respective commits
from there. But with salsa this was sufficiently easy and with syntax
issues of d/u/metadata now dealt with I need to think more about what
other uses cases of that local Debian Med mirror there are - btw, it
Debian Med is 43GB of git repos, master branch only.

Cheers,
Steffen