Am I able to use dynamic parameters in libraries configuration files? I have hard coded GMaps API key in URL inside in the libraries.yml file.

Would I be able to use a dynamic parameter for this key?
You should be able to use hook_library_info_build(). It's a new (to D8) hook that allows you to define libraries at runtime.
Here's the change record that talks about it's introduction. It's unlikely to go anywhere, but here's the description from the change record:

There was no way to dynamically register libraries. Using hook_library_info_alter() to register new library is possible but doesn't end well in alter/weight.
Therefore a new hook is created namely hook_library_info_build()

Alternatively; you could potentially add the hook as normal in your example.libraries.yml file, and then use hook_library_info_alter.