Support "usages" as a data-driven way to document how to consume an artifact for a user

[EricWittmann]

A nice feature in the UI would be a section for "Usage" - similar to what API documentation generators and maven central provide:

Originally I was thinking we should do something similar just in the UI, but it might be more powerful to make it data-driven and user defined. We could have a new collection in the Registry API like:

/usages

This would be a collection of templates that could be managed by admins of the registry. The UI could pull these templates in order to display customized "usage" information for each artifact. Some possible default "usage" templates might be:

• shell/curl
• Java (plain)
• Java (kafka serdes)
• Apicurio Registry maven plugin

Then admin users could provide their own by POSTing to the /usages endpoint, which is useful if e.g. they are using registry in a .NET or python environment.

[EricWittmann]

Looking for discussion on this from @alesj @carlesarnal @jsenko :)