Add and update GitLab templates

Description

• Feature requests should be made in Discourse, but some repos don't mention that Also, some repos:

• Don't have any templates

• Have templates but don't have a default one to inform people which templates should be used

• Have incomplete templates

Goals

Help making bug triages easier.

Scope

Core, development, World (?) apps

People on charge & contact

Instructions to achieve the goals

Label for tracking the initiative

Template models

• Feature.md

• Bug.md

• Default.md

List of projects & tasks

• Create missing app tags in Discourse

• Baobab (Disk Analyzer)

• Boxes

• Builder

• Calculator

• Characters

• Clocks

• Console

• dconf-editor

• Disks

• Evince

• Eye of GNOME

• Fonts

• GIMP (see: gimp!1412 (merged))

• GTK (?)

• Initial Setup

• Music

• Mutter (?)

• Nautilus

• Logs

• Settings: gnome-control-center!1627 (closed)

• Shell: gnome-shell!2605 (closed)

• Software

• System Monitor

• Text Editor

• Totem

• Tweaks: gnome-tweaks!108 (closed)

• Yelp

How can I help

• Find a repo that doesn't have templates or have outdated templates
• Propose a merge request