Camera definition files should support xz compression (mavlink#1355)

message_definitions/v1.0/common.xml

@@ -6020,7 +6020,7 @@
       <field type="uint8_t" name="lens_id">Reserved for a lens ID</field>
       <field type="uint32_t" name="flags" enum="CAMERA_CAP_FLAGS" display="bitmask">Bitmap of camera capability flags.</field>
       <field type="uint16_t" name="cam_definition_version">Camera definition version (iteration)</field>
-      <field type="char[140]" name="cam_definition_uri">Camera definition URI (if any, otherwise only basic functions will be available). HTTP- (http://) and MAVLink FTP- (mavlinkftp://) formatted URIs are allowed (and both must be supported by any GCS that implements the Camera Protocol).</field>
+      <field type="char[140]" name="cam_definition_uri">Camera definition URI (if any, otherwise only basic functions will be available). HTTP- (http://) and MAVLink FTP- (mavlinkftp://) formatted URIs are allowed (and both must be supported by any GCS that implements the Camera Protocol). The definition file may be xz compressed, which will be indicated by the file extension .xml.xz (a GCS that implements the protocol must support decompressing the file).</field>
     </message>
     <message id="260" name="CAMERA_SETTINGS">
       <description>Settings of a camera. Can be requested with a MAV_CMD_REQUEST_MESSAGE command.</description>