Changes to Fetch matched event clusters

the query request parameter relation was restricted to a list of enum values

for the query request parameter relation, default value identity was added

for the query request parameter relations, default value identity was added

added the new optional query request parameter category

added the new optional query request parameter query

added the new enum value disjoint to the query request parameter relation

added the new enum value identity to the query request parameter relation

added the new enum value overlap to the query request parameter relation

added the new enum value subset to the query request parameter relation

added the new enum value superset to the query request parameter relation

endpoint added