[REST API] Created a /search/versions endpoint

[EricWittmann]

This allows searching for versions across all groups and artifacts. It has two variants:

• GET - standard search versions using query param filters
• POST - search for versions by content

The latter variant also replaces the old way of figuring out which version of an artifact uses specific content, which was semantically problematic and existed here:

POST /groups/:groupId/artifacts/:artifactId

That operation has been removed. Now if you need to find an artifact version by content you must use the POST variant of /search/versions and include groupId and artifactId filter query params (along with optional sorting and limiting params). It's much more flexible and I think makes a lot more sense semantically.

Note that I also renamed type properties in the REST API definition to artifactType since we've done the same for all our IDs. It seems redundant but I think adds clarity.

[apicurio-bot]

Thank you for creating a pull request!

Pinging @jsenko to respond or triage.