Pass Raygun package version in Crash Reporting payload in RaygunClientMessage

[miquelbeltran]

Currently the version property is not set. Look for a way to load this value from the pubspec.yaml.

[miquelbeltran]

Using package_info_plus won't work, because that reads the package from the "app" that uses the package, not from the package itself.

[TheRealAgentK]

It might just have to be a constant for now and changed as part of the release process for a new version.