I18N JS files starting with c or d

This is one of many MRs opened in order to improve the overall
internationalisation of the GitLab codebase.

This commit only targets Vanilla JS files.

i18n documentation
https://docs.gitlab.com/ee/development/i18n/externalization.html

locale/gitlab.pot

@@ -1540,6 +1540,14 @@ msgstr ""
 msgid "Attach a file by drag & drop or %{upload_link}"
 msgstr ""
 
+msgid "Attaching a file"
+msgid_plural "Attaching %d files"
+msgstr[0] ""
+msgstr[1] ""
+
+msgid "Attaching the file failed."
+msgstr ""
+
 msgid "Audit Events"
 msgstr ""