feat: add proc macro to reduce overseer mock boilerplate (#2949)

polkadot/node/overseer/subsystems-gen/tests/ui/err-01-enum.rs

@@ -0,0 +1,13 @@
+#![allow(dead_code)]
+
+use polkadot_procmacro_overseer_subsystems_gen::AllSubsystemsGen;
+
+#[derive(Clone, AllSubsystemsGen)]
+enum AllSubsystems<A,B> {
+	A(A),
+	B(B),
+}
+
+fn main() {
+	let all = AllSubsystems::<u8,u16>::A(0u8);
+}