add gitlab templates

.gitlab/issue_templates/Bug.md

+# Environment info
+
+<!-- Everything is optional and where applicable but the more information the better. -->
+* Browser, version, OS, platform:
+* Instance URL:
+* Frontend version (see settings -> about):
+* Backend version (see settings -> about):
+* Browser extensions (ublock, rikaichamp etc):
+* Known instance/user customizations (i.e. pleromafe mods/forks, instance styles etc)
+
+# Bug description & reproduction steps
+
+<!-- Type out here how to reproduce the bug, what goes wrong and what should go right -->
+<!-- Screenshots and videos help a lot ;) any observations might also help -->
+<!-- Also mention if there any errors in browser's console if relevant -->
+
+# Bug seriousness
+
+<!-- Everything is optional and free-form -->
+* How annoying it is:
+* How often does it happen:
+* How many people does it affect:
+* Is there a workaround for it:
+
+/label ~Bug