sp-utils => sc-utils (#9677)

* sp-utils => sc-utils

* cargo fmt

* These files are now in the client so should be licensed as GPL3

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/client/utils/README.md

@@ -0,0 +1,20 @@
+Utilities Primitives for Substrate
+
+## Features
+
+### metered
+
+This feature changes the behaviour of the function `mpsc::tracing_unbounded`.
+With the disabled feature this function is an alias to `futures::channel::mpsc::unbounded`.
+However, when the feature is enabled it creates wrapper types to `UnboundedSender<T>`
+and `UnboundedReceiver<T>` to register every `send`/`received`/`dropped` action happened on
+the channel.
+
+Also this feature creates and registers a prometheus vector with name `unbounded_channel_len` and labels:
+
+| Label        | Description                                   |
+| ------------ | --------------------------------------------- |
+| entity       | Name of channel passed to `tracing_unbounded` |
+| action       | One of `send`/`received`/`dropped`            |
+
+License: Apache-2.0