gui, script: Translate discovery popover and detect it in translate script

Skip-check: pr-solaris

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4061

gui/default/assets/lang/lang-en.json

@@ -30,6 +30,7 @@
    "CPU Utilization": "CPU Utilization",
    "Changelog": "Changelog",
    "Clean out after": "Clean out after",
+   "Click to see discovery failures": "Click to see discovery failures",
    "Close": "Close",
    "Command": "Command",
    "Comment, when used at the start of a line": "Comment, when used at the start of a line",