Plugin Support

[tconley1428]

What was changed

Added a new Plugin concept for configuring clients and workers

Why?

Many users need to do a common set of configurations across multiple locations, or provide such a configuration set to others.

Checklist

1. Closes [Feature Request] Plugins to support controlling multiple configuration points at once #950

2. How was this tested:
   New set of tests in test_plugins.py

3. Any docs updates needed?
   Readme is updated, docs will be needed.

[dandavison]

This is great.

I spent some time seeing if we could improve any of the names in the interface.

What I'd like to suggest there is: instead of on_create_client and on_create_worker, how about

def client_config(self, config: ClientConfig) -> ClientConfig

def worker_config(self, config: WorkerConfig) -> WorkerConfig

An alternative that was mentioned on slack was configure_client() / configure_worker(). That could work too, but it kind of suggests that the method gets to instantiate or mutate a client/worker. I like the simplicity of client_config(self, config: ClientConfig) -> ClientConfig: it makes it clear that your job in that method is to return the config you want, nothing less and nothing more.

on_create_client and on_create_worker don't work as well because their names suggest an event that occurs after or during instantiation of the client/worker, which is awkward seeing as the method is a pure transformation of a config struct and so is clearly happening before instantiation.

Other than that, it took me a bit of time to understand why the multiple inheritance made sense, and why it made sense to expose the "service client" rather than just "connect client", but I think this all makes sense and is very natural given the SDK's existing public interceptor API.

[cretz]

Overall agree w/ @dandavison

An alternative that was mentioned on slack was configure_client() / configure_worker(). That could work too, but it kind of suggests that the method gets to instantiate or mutate a client/worker

I think it suggests the method gets to configure the client/worker, not instantiate or mutate it. I think it's clearer than the getter-looking ones that are missing the verb.

[dandavison]

configure_client() / configure_worker()

Yes I think I've changed my mind, I prefer these also.

[cretz]

LGTM, nothing blocking