Implement reaction editing capabilities. A reaction may only be edited by its owner/author (and a moderator, in case moderation is to be implemented). Only the message can be edited.
[x] GraphQL: mutations.EditReaction
[x] Store: transactions: EditReaction
[x] API test: mutations.EditReaction
[x] API test: mutations.EditReaction (invalid input)
[x] API test: mutations.EditReaction (authorization)
Implement reaction editing capabilities. A reaction may only be edited by its owner/author (and a moderator, in case moderation is to be implemented). Only the message can be edited.