Add GA release build command

[ryanjbaxter]

Add releaser.[maven | gradle | bash].ga-release-build-command. This command will only be used for non-snapshot, non-milestone, and non-rc releases (aka GA releases). In the case were it is not a GA release or the property is not set we use releaser.[maven | gradle | bash].release-build-command (the same command we use today).

This should enable projects to have a specific build command used when doing a GA release, enabling them to skip tests if they want.