When replaying multiple, only send unique records to retry topic

[MitchelNijdam-Rockstars]

When for whatever reason there are two records in DLQ for the same original kafka record (that is, same key & value & kafkatimestamp & original offset), while replaying it doesn't make sense to put duplicate records on the retry topic.

So, when replaying, deduplicate first. This can be either default behavior or API parameter ...?unique=true.

In the response of replay endpoint, might be good to show that certain messages were not send because of duplicate, e.g.:

    "replayed": [
        {
            "originalOffset": 23629,
            "replayedOffset": 1
        }
    ],
    "ignored": [
        {
            "originalOffset": 23630,
            "reason": "duplicate of 23629"
        }
    ],...