Add a profile to handle external references

[jyutzler]

We don't currently have a way to deal with relationships between base data and related data that lives outside the GeoPackage. In theory this could be supported through a URI, but the details of doing this have not been specified.

[bradh]

This would be fairly easy to do, but this isn't a great fit for GeoPackage, which is better suited to offline use, and avoiding dependence on a particular network.

Do we have a specific use case that needs this? Is there an advocate for the requirement?

[jyutzler]

moved to ☝️