CMake install target should stage external_control.urscript

[acmorrow]

Feature summary

Much like the build currently installs package.xml, it should probably also install external_control.urscript.

In our project making use of the Universal_Robot_Client_Library, our built software includes a copy of external_control.urscript. However, obtaining it at build time requires us to reach into the sources as obtained with FetchContent.

It would be easier if the URCL library install target just staged this file somewhere (probably under share per GNUInstallDirs). Then we would know to find it in the share directory at runtime, rather than needing to find the file and copy it ourselves.

I think this is fairly easy, probably just a few lines of CMake. I'd be happy to put together a PR, but I wanted to make an issue first to (hopefully) get buy in on the idea.

Tasks

To complete this issue involves

• Implement the feature
• Make documentation
• Make Unit test
• Make example
• Test on real hardware

[urfeex]

I think, that's a very valid idea. If you're even up to make a PR for that, we will be happy to review it.