Enable publication of api docs of sensors, formatter and faces libraries on api.kde.org

docs/Doxyfile.local

+EXCLUDE_PATTERNS = */faces/facepackages \
+                    */faces/import/SensorFace.qml # Document SensorFace via SenorFace_p.h

metainfo.yaml

+fancname: Libksysguard
+description: Library to retrieve and display information on the current status of computer hardware
+irc: plasma
+maintainer: ahiemstra
+platforms:
+    - name: Linux
+    - name: FreeBSD
+public_lib: true
+public_source_dirs:
+    - faces
+    - sensors
+    - formatter
+libraries:
+    - KSysGuard::SensorFaces
+    - KSysGuard::Sensors
+    - KSysGuard::Formatter