Support both old and new module versions in the module registry

[f0ssel]

We need to decide on and implement how we can support serving old module versions from the coder/modules repo alongside new versions of those modules in the coder/registry repo. This includes handling the case where a module is moving from being hosted under the coder namespace to the partner or contributors namespace.

Some notes:

• Because the module registry protocol has a service discover endpoint we could make a new version of the API using the new user namespaces and have the service discovery point to that if we want
• We can also just move the modules to the new user namespaces and continue to serve the old versions from the coder namespace
• We may be able to do some sort of hardcoded redirect for those modules to point to the new user namespace if terraform respects this, need to test