Improve building of nested plugins

[tolzhabayev]

What would you like to be added:
Currently nested plugins are built by default in the main dist folder which forces developers to use relative paths in their executable properties. (Example)

If the relative path is changed to a non-relative one mage fails with:
Error: datasource should reference executable in root folder (source)

We should improve the build script so that it can also build executables in sub-folders without a need to put everything into the root folder and use relative paths.

Here is a workaround some developers are using: https://github.com/performancecopilot/grafana-pcp/blob/main/Makefile#L61-L69

Why is this needed:
The status quo causes issues with windows installations as they can not resolve the relative path properly.