Support for custom registries

[vegastyle]

Currently OpenPackage has hardcoded the address for the registry. This makes it so that you can't self host your own packages outside of a local folder. The package should support allowing you to set a different registry or list of registries to target besides the official registry.

Ideally it should support the following:

• a --registry flag for setting a registry to override the current registry per call
• add an indexes/registry field to the config that allows you to set globally the registry to target. It should also allow

PyPi imiplementation:
https://devpi.net/docs/devpi/devpi/latest/+d/quickstart-pypimirror.html#permanent-index-configuration-for-pip

[hyericlee]

Makes sense, thanks for the feedback!

I'll need to work out the finer details (endpoints and DTOs to be specific) as OpenPackage has nuances that slightly differ from traditional package managers.

Will define a unified protocol for upcoming releases.