closes #503

This PR adds the trait InspectorCliExt, which allows a user to define a function that initializes and returns their custom inspectors.

Future proofing the public api - In order to keep the diff small and not over engineer for a problem we don't currently have, I avoided making a super trait for all cli extensions. However I think a super trait could help reduce the churn for brontes lib consumers and it might be wise to add sooner then later. For example we could have a trait

trait CliExt {
   type Inspector: InspectorCliExt;
   
   // Future assoiated types with default impls 
   // could be added here, minimizing the changeset for 
   // lib consumers to upgrade e.g. they avoid having to thread
   // additional generic type params across the cli code when
   // we add an additional ext trait
}
impl CliExt for () {
  type Inspector = NoopInspectorCliExt;
}

Proposed follow ups:

• Add example - I already have a wip here https://github.com/emostov/brontes/pull/1 (lmk if you can't see it, I just needed to do it in my fork so I could target this branch)
  • An example could be good for adding some cheap sanity check test such as checking for initialized custom inspectors logging to stdout
• Add a .env.sample to help people boot strap a local setup. Relates to Write documentation  #205,  specifically "Installation and setup instructions"
• Expose public Cli struct that can wraps up the logic of calling Arg::parse and run, the ext trait could be an arg directly to the struct.
• Ensure that panic messages make their way to tracing subscriber or at least stdout/stderr. It appears panic messages get squashed, which is especially burdensome because a lot of initialization logic uses unwraps/expects and it can be hard to debug. For example, the default impl for ClickHouseConfig (which is implicitly called by Clickhouse::default) will panic if certain env vars are not set, but the expect messages don't make their way to the terminal. This

Didn't want to spam with issues, but happy to break these out if they look reasonable

TODO

• tests
• rust docs example for trait impl