Support a task query in `TaskModule.defaultTask`

[lefou]

It would be nice, if one could return a task in a sub-module from defaultTask.

Example:

object example extends TaskModule {

  def defaultTask() = "foo.bar.testForked"

  trait MyTest extends TestModule {
    ..
  }

  object foo extends Module {
    object bar extends MyTest
    object baz extends MyTest
  }

}

Bonus, if we also support a wildcard query:

  def defaultTask() = "foo._.testForked"

[lefou]

My typical workaround is to add a forwarder task,but that's cumbersome and boilerplate-y.

https://github.com/lefou/mill-vcs-version/blob/13359114747338d5b490499daed5b409d8f5292b/build.sc#L153-L157

// Mill 0.11
object itest extends Cross[ItestCross](millItestVersions.map(_._1)) with TaskModule {
  override def defaultCommandName(): String = "test"
  def testCached: T[Seq[TestCase]] = itest(millItestVersions.map(_._1).head).testCached
  def test(args: String*): Command[Seq[TestCase]] = itest(millItestVersions.map(_._1).head).test(args: _*)
}