Add more permissive fire-and-forget effect (#427)

* Add more permissive fire-and-forget effect

* Update Effect.swift

* Update Effect.swift

Author: stephencelis

Sources/ComposableArchitecture/Effect.swift

@@ -333,4 +333,22 @@ extension Publisher {
       .catch { Just(.failure($0)) }
       .eraseToEffect()
   }
+
+  /// Turns any publisher into an `Effect` for any output and failure type by ignoring all output
+  /// and any failure.
+  ///
+  /// This is useful for times you want to fire off an effect but don't want to feed any data back
+  /// into the system.
+  ///
+  ///     case .buttonTapped:
+  ///       return analyticsClient.track("Button Tapped")
+  ///         .fireAndForget()
+  ///
+  /// - Returns: An effect that never produces output or errors.
+  public func fireAndForget<NewOutput, NewFailure>() -> Effect<NewOutput, NewFailure> {
+    return self
+      .flatMap { _ in Empty() }
+      .catch { _ in Empty() }
+      .eraseToEffect()
+  }
 }