Add a unittest / integration test to make sure that `colcon-cargo` works as part of a `colcon-build`

[bergercookie]

Such test should include the following step:

• Create a template ws/src/ directory with a minimal rust package (hello-world)
• Run colcon (with the colcon-cargo extension enabled) from the root of the workspace and make sure that the appropriate binaries are generated under the rust package install prefix; Potentially also execute the installed executable