Scope to install the "common" XMLs from sros2/test/policies/common?

[aprotyas]

Feature request

Feature description

Is it possible to rearrange the structure of the repository such that the "common" XML files under sros2/test/policies/common are installed and accessible through importlib/the ament resource index?
I am writing a nodl_to_policy tool, that generates ROS 2 access control policies from their corresponding NoDL description files. In that conversion, each node in the ROS graph receives default permissions for a common set of services/topics/actions, and this common set is described in the XML files under sros2/test/policies/common. In adhering to DRY principles, I would like not to repeat these same "common" resources within the nodl_to_policy tree, but rather access said files through importlib/the ament resource index.

Implementation considerations

Move the entire sros2/test/policies subtree to sros2/data/policies? I'm not sure how that affects the rest of the testing, but I can gladly poke into it.

[mikaelarguedas]

I believe the intent of #147 was to provide plumbing for this. It seems that it's been stale for a long time though, if you have time / opportunity of picking it up it would be a better way of resolving this issue.

The other "test" policies do not belong in the install folder IMO as they are just examples and should be provided by the packages providing the corresponding nodes and not by sros2