Move config install location

The configs are currently placed in install/config, without any prefix. This might conflict with other packages' configurations. I don't know what ROS's standard placement is, but likely either in share, or in a subdirectory of config.

Start by locating the install/config handling in the repository's build-support macros and check how the current unprefixed path is produced. Compare the available ROS placement conventions, then verify that installation uses a non-conflicting location and that existing configuration consumers still find it.

Written by the indexing model from the issue text.