Add rmw_fastrtps_dynamic_cpp to the explicit group deps (#177)

This package, which is in the same repository as rmw_fastrtps_cpp,
declares itself as a member of the rmw_implementation_packages group.
Fore completeness, and also because it is necessary for preresolved
groups to be comprehensive for RPM packaging purposes, the explicit
group list should contain this package.

Signed-off-by: Scott K Logan <logans@cottsay.net>

rmw_implementation/package.xml

@@ -23,6 +23,7 @@
   <build_depend>rmw_connext_cpp</build_depend>
   <build_depend>rmw_cyclonedds_cpp</build_depend>
   <build_depend>rmw_fastrtps_cpp</build_depend>
+  <build_depend>rmw_fastrtps_dynamic_cpp</build_depend>
   <!-- end of group dependencies added for bloom -->
 
   <depend>rmw_implementation_cmake</depend>