Use "handled" instead of "responded" for checkmark message

Very often it is the case that crew member does not really respond on the ticket, but wants to add a reaction to signal to others that the ticket is handled. Example case is that someone else (maybe not outside of crew) responded on the ticket.

In these cases responded is not really correct anymore and people feel weird when adding the reaction and seeing such message.

I hence propose to change the wording to handled as that can imply both responding but also finding someone else to respond, as crew members are primarily custodians of the queue.

Another alternative I see is verified.

Example recent discussion around this: https://gitlab.slack.com/archives/C01AEL6E207/p1621322674008300