Support downloading additional artifacts (sources, javadoc, etc.)

fixtures/projects/artifacts/sources-javadoc/kotlin/build.gradle.kts

@@ -0,0 +1,14 @@
+plugins {
+    java
+}
+
+repositories {
+    maven {
+        url = uri(System.getProperty("org.nixos.gradle2nix.m2"))
+        isAllowInsecureProtocol = true
+    }
+}
+
+dependencies {
+    implementation("org.jetbrains:dummy:0.1.2")
+}