Add a CEP for hooks that will enable fetch (i.e. networking) plugins

[travishathaway]

Exploratory work is current underway for providing a series of hooks that will enable third parties to override how conda does its networking:

• Fetch Plugin Hook conda#11821

With this CEP, we aim to clearly articulate our arguments for doing this in an effort to get consensus from the steering council. This CEP will outline the new plugin hooks that we would like to add to conda as well as a full explanation of how they work and what there intended uses will be.

⚠️ This work is still being actively researched. All findings about what this particular CEP will need will be added here as comments.