add configuration for custom pkg names

[lukaszx0]

When not using fully qualified url package names (eg mod foobar instead of mod github.com/foo/bar), the code that strips the package from the path strips too much of it.

This change leaves the default behavior unchanged (stripping github.com/owner/repo) and adds ability to configure custom package name to make path stripping work correctly with custom module names.

[lukaszx0]

Actually, it's called module in go mod, eg:

module foobar

go 1.15

so we can rename it to module-name