Describe the bug
This is related with #25
Several maven artifact does not provide license info on POM (such as retrofit, moshi and etc.. )
Also, several libraries can be included as non-maven artifact. (especially native libraries )

So it needs to add licenses manually, but oss-licenses-plugin does not allow.

Additional context
I made dirty modification to add licenses manually.
https://github.com/ganadist/play-services-plugins/tree/support_third_party_licenses

Just put license content under third_party_licenses directory at root project, and plugin will generate license item with filename