helper function for wrap-model-fill-assoc

(process-fill-assoc {:age 10} {:name “Chris”, :age 9} :account {} {:fill-assoc {:account {:age 10}}} {}) => {:name “Chris”, :age #{9 10}}

adds an additional value to the entry

(graph/normalise {:account/name “Chris” :account/age 9} {:schema (schema/schema examples/account-name-age-sex) :pipeline {:fill-assoc {:account {:age 10}}}} {:normalise wrap-model-fill-assoc}) => {:account {:name “Chris”, :age #{9 10}}}