Error check parameterized search arguments against OpenSearch mappings

[kburke]

Parameterized searches allow exact match attribute values to be specified as GET parameters, but the initial implementation simply passed them all to OpenSearch in a QDSL query. This can easily result in "zero documents" returned if a specified parameter is not an exact match to an OpenSearch attribute.

search-api's /attribute-values endpoint already works with OpenSearch's _mappings call to identify keywords as part of its task. Extend or re-use this capability to verify user input to /param-search requests.