add better error messaging upon rules collection creation

[depahelix2021]

If you do not provide both names, there should be a clear error message that says as much.

If a 500 Internal Server Error comes back, surface that to the user and hint that it is most likely because they are trying to create a rules collection for a Solr collection that already has one attached to it.

[epugh]

Error handling makes sense, however I wonder if there is also a better response code that the API could provide?

[depahelix2021]

Now instead of a 500, the API catches that issue with SQL constraints not allowing the addition, and returns back a more normal BadRequest.