feat(extension-system): transport now extensible

[jasonkuhrt]

No description provided.

[jasonkuhrt]

Update:

The major problem right now is TypeScript performance. I need to optimize things.

Inference is probably the number 1 culprit.

I could improve things here:

1. Define the request pipeline with static types
2. Define the extensions with static types

It is ugly but contained and clear. I just need to figure out the API for supplying the pre-built types.

Other ideas:

• Is the ConfigManager utility leading to performance issues?
• Can we make use of more interfaces and less type aliases?
• Look for ways to simplify the extension type system