Allow usingInitScript(Consumer) for inline configuration of init script

[lacasseio]

Instead of:

def initScriptFile = file('init.gradle')
initScriptFile << configurePluginClasspathAsInitScriptDependencies() << '''
    apply plugin: dev.nokee.init.NokeeInitPlugin
'''
executer = executer.usingInitScript(initScriptFile).

we could have something like:

executer = executer.usingInitScript(nokeeInitScript())

private static Consumer<InitScriptBuilder> nokeeInitScript() {
  return builder -> builder.inDirectoryAt('init.gradle').configurePluginClasspathAsInitScriptDependencies().applyPlugin('dev.nokee.init.NokeeInitPlugin')
}

The InitScript builder would allow setting the init script in the init.d directory if needed but would also fail if using a shared directory.

[lacasseio]

An experimentation of this work is under Nokee, there are still quite a bit of open questions so we will unscheduled it for now.