Make vertx worker pool size configurable

[jframe]

PR Description

Make vertx worker pool size configurable. Web3Signer uses the worker pool for signing requests. Increasing the size of the pool might help if there is a spike in signing requests.

It can be configured by using the hidden option --Xworker-pool-size --vertx-worker-pool-size option.

Default is set to the same the default in Vertx which is 20. See https://vertx.io/docs/apidocs/io/vertx/core/VertxOptions.html#DEFAULT_WORKER_POOL_SIZE

Fixed Issue(s)

Documentation

• [x] I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• [x] I thought about adding a changelog entry, and added one if I deemed necessary.

Testing

• [ ] I thought about testing these changes in a realistic/non-local environment.

[jframe]

LGTM. Do we need code to make the config and env vars work or is that just for the ATs?

That's just for ATs. We automatically get env and config through pico environment providers.