Convert models to plugins, remove hardcoded model string checks

Problem/Motivation

BedrockProvider loads config for a model via hardcoded strings, this makes it very difficult to add new models without either swapping this class out or patching the module.

We should turn the models into plugins and provide some interfaces to make this easier to extend.

Steps to reproduce

Try add a new model that doesn't have one of the strings in BedrockProvider. See it doesn't get called.

Proposed resolution

Add a plugin manager for the models
Add some interfaces to ensure the models have a defined contract.

Remaining tasks

Do the work
Review
Merge

User interface changes

N/A

API changes

New interfaces introduced
Models are now plugins

Data model changes

N/A