move issue filters to shared template (#25729)

Issue filters are being used on repo list page and on milestone issues
page, and the code is mostly duplicated.

This PR does the following changes:
- move issue filters into a shared template
- allow filtering milestone issues by project, so no need to hide this
filter on milestone issues page
- remove some dead code (e. g. issue actions in milestone issues
template)
- fix label filter dropdown width

---------

Co-authored-by: 6543 <6543@obermui.de>

web_src/css/repo.css

@@ -169,6 +169,7 @@
 
 /* the label-filter is the first dropdown, it shouldn't be shown leftward, otherwise it may go out the viewport (left side) */
 .repository .filter.menu .ui.dropdown.label-filter .menu {
+  min-width: max-content;
   right: unset;
   left: 0;
 }