Create an extensible bridge worker with identical APIs

[ghostwriternr]

Users should be able to deploy the bridge worker to their user account, and get REST APIs for accessing sandboxes on their account. Alongside this, also export a client SDK that is 1:1 identical with the current API exposed to workers, but with a different entrypoint that is not dependent on the durable object namespace and instead uses the worker endpoint to connect.

[ghostwriternr]

Marking this issue as being blocked by #285 because there are lots of unknowns about how to bridge the lifecycle of the current containers platform, wherein 1. Durable Object namespace bindings have to be created for each unique container application (typically, mandated by unique container implementations) and 2. such configurations need to be uniquely 'deployed' using wrangler. Potentially, in the long run, we're able to construct container images on the fly and schedule them to run, but that is not in a short-term roadmap.