/usr/share/kcmsolidactions/solid-action-template.desktop is in plasma-desktop-data 4:5.12.4-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 | [Desktop Entry]
Actions=open;
Type=Service
X-KDE-Action-Custom=true
X-KDE-Solid-Predicate=[ IS StorageVolume AND StorageVolume.ignored == false ]
[Desktop Action open]
Icon=unknown
Exec=
|