Add queued_outgoing_messages panel for grafana

[syjn99]

This PR Addresses #12254. Added queued_outgoing_messages per second next to Incoming Gossip and Requests panel. The expression looks like:

"rate(reth_network_queued_outgoing_messages{instance=\"$instance\"}[$__rate_interval])"

[mattsse]

this does a lot more than adding a new panel, so not sure how to best review this

can we limit this pr to the additional panel?

@Rjected

[syjn99]

@mattsse Seems like plugin version is bumped, and its diff is included. I pushed new commit so that reviewing this code would be much easier.

[Rjected]

this looks good to me, do you mind adding a screenshot of the panel?

[syjn99]

Here's a partial screenshot of the dashboard. New panel is next to Incoming Gossip and Requests panel. Ran clients for few hours, on ephemery network with fuzzing with tx fuzzer.
As there are no queued messages, the panel looks flat. Does this look good to you?

[Rjected]

nice lgtm