Add missing HermesMockExpect documentation

[3750]

This PR adds missing documentation for

hermes/hermes-mock/src/main/java/pl/allegro/tech/hermes/mock/HermesMockExpect.java

Line 45 in c817e32

public <T> void jsonMessagesOnTopicAs(String topicName, int count, Class<T> clazz, Predicate<T> predicate) {

and for

hermes/hermes-mock/src/main/java/pl/allegro/tech/hermes/mock/HermesMockExpect.java

Line 53 in c817e32

public <T> void avroMessagesOnTopic(String topicName, int count, Schema schema, Class<T> clazz, Predicate<T> predicate) {