Add initial implementation for running SBT commands.

testing/resources/sbt_repo_with_touch_command/project/TouchCommand.scala

@@ -0,0 +1,13 @@
+import sbt.Command
+
+import java.nio.file.{Files, Paths}
+
+object TouchCommand {
+  def touchCommand = Command.args("touch", "args") { (state, args) =>
+    args.map(Paths.get(_).toAbsolutePath).foreach { path =>
+      println(f"Creating file: $path")
+      Files.createFile(path)
+    }
+    state
+  }
+}