mod-kb-ebsco - consistent use of HTTP 400 vs 422 status code

While writing API tests for mod-kb-ebsco we found some inconsistency in when HTTP status code 422 is used vs HTTP status code 400.

For example
POST /eholdings/titles with an invalid name returns an HTTP status code 422
PUT /eholdings/resources with an invalid name returns an HTTP status code 400

This could be due to returning error information as a passthrough from rm api vs directly detecting the error in mod-kb-ebsco.

Would be helpful to review status codes that are returned to be sure they are consistent and predictable.