Include metadata in merge reply begin ex

[akrambek]

We should include metadata as part of merge reply begin ex

read zilla:begin.ext ${kafka:matchBeginEx()
                               .typeId(zilla:id("kafka"))
                               .merged()
                                   .capabilities("FETCH_ONLY")
                                   .topic("test")
                                   .partition(0, 2, 2, 2, "test-meta")
                                   .build()
                               .build()}