Create "virtual artifact" feature, allowing redirects/linking functionality

[EricWittmann]

This feature is to allow users to create a virtual artifact or version that links to an actual artifact/version. The main use-case is to recover from deleted content. When deleting a version (for example) the content at a given globalId will be gone from the registry. If kafka messages exist that refer to that globalId, they will be impossible to consume because the schema at the globalId will be missing.

This feature will allow users to fix the problem by re-registering the missing schema and then creating a virtual link from the old globalId to the new one.