Add a global_module example

[robertek]

This example shows how to create global configuration module that may be used anywhere in the code with predefined interface.

[softdevca]

This should be updated to use OnceLock instead of lazy_static. See pr #515

[robertek]

Thanks for pointing that out.

I have updated that and added a comments around.

[softdevca]

I made some small improvements to make clippy happy at https://github.com/fork-in-the-code/fitc-config/commit/374840a4786ed6a66eb52f5d0b321c72cb37aae9

[robertek]

Thanks for the review. I've applied that change.