Fix missing exec_depends in package.xmls and docstrings to generate documentation without any warnings using autodoc

Note: Works for all pkgs here except launch_ros.

  File "/home/yadunund/ws_rolling/src/ros2/launch_ros/launch_ros/launch_ros/parameters_type.py", line 50, in <module>
    SomeSubstitutionsType_types_tuple +
TypeError: unsupported operand type(s) for +: 'SomeSubstitutionsType_types_tuple' and 'tuple'

Might be able to fid this if we modify the code to explictly cast tuple(SomeSubstitutionsType_types_tuple) as autodoc is unable to infer the type given that the dep modules are not imported.

Incomplete documentation will be generated as a result for launch_ros