fix install location of plugin manifest xml

[knorth55]

This PR fixes install location of plugin xml.
Current cmake means that plugin xml will be installed to share directory, which cause plugin load error.

/opt/ros/noetic/share/prosilica_camera$ ls
cmake  launch  nodelet_plugins.xml  package.xml  prosilica.launch  streaming.launch
/opt/ros/noetic/share/prosilica_camera$ ls nodelet_plugins.xml 
nodelet_plugins.xml

Plugin manifest xml should be share/plugins.

prosilica_driver/prosilica_camera/package.xml

Line 47 in 3991df7

<nodelet plugin="${prefix}/plugins/nodelet_plugins.xml" />

I change to install the manifest xml to correct path in cmake.