Add metrics for dropped outgoing messages

[mattsse]

Describe the feature

session channels are bounded, if there's no capacity, the message will be dropped:

reth/crates/net/network/src/session/mod.rs

Line 349 in 63c71cf

let _ = session.commands_to_session.try_send(SessionCommand::Message(msg));

it would be nice to have a counter for when this happens

reth/crates/net/network/src/metrics.rs

Line 83 in 63c71cf

pub struct SessionManagerMetrics {

TODO

• add new metrics counter, increase if the message couldn't be delivered

Additional context

No response

[nkysg]

Please assign me.

[malik672]

Please assign me.

you should add the tag

[nkysg]

Please assign me.

you should add the tag

I have no permissions to add the tag.

[mattsse]

cool, thanks @nkysg, please always simply comment, otherwise github doesn't let me assign...

[nkysg]

@mattsse got it.