Add trait for configuring GasNow WebSocket error reporting

[nlordell]

This PR adds a trait for reporting errors in the gas now WebSocket-based gas price estimator. This way, we can configure custom error handling (such as adding metrics) in gp-v2-services as well as remove some of the pesky error alerts we were seeing.

Test Plan

Not sure what to run, just did cargo fmt -- --check && cargo clippy --all-features --all-targets && cargo test.

[vkgnosis]

Seems fine although the fact that we need it is an indication that this component should move back into the main repo to me.

[bh2smith]

I was looking around in gp-v2-services all day for some indication of what was causing either of these two alerts

[DFUSION][GP-V2-SERVICES] Error
ERROR (pod: dev-dfusion-v2-solver-mainnet-dc6549cf-chhzq):
2021-09-06T20:44:02.871Z ERROR gas_estimation::gasnow_websocket: websocket stream timed out

[DFUSION][GP-V2-SERVICES] Error
ERROR (pod: dev-dfusion-v2-solver-mainnet-dc6549cf-chhzq):
2021-09-07T07:11:19.768Z ERROR gas_estimation::gasnow_websocket: websocket stream failed err=Protocol(ResetWithoutClosingHandshake)

Looks like this PR intended to be a first step at dealing with these. I actually didn't even know this repo existed until I was notified about this PR.

[nlordell]

Seems fine although the fact that we need it is an indication that this component should move back into the main repo to me.

Created #11.

I don't disagree. I also found that its not super general and specific to how we use it in services. Merging for now to silence alerts.