Add a slash command /remind to remind me about an issue or MR
Description
Problem: there may be a MR or issue that I want shepherd / follow to completion but that either (a) has a lot of activity which overloads my inbox if I'm "subscribed" or (b) doesn't have a guarantee of being touched in a way that will tag me or create a todo for me.
Proposal
Slack has a great feature for this - slackbot reminders in the form of a slash command such as:
/remind [@someone or #channel] [what] [when]
A simpler iteration 1 style implementation for GitLab might be, on an issue or MR I say:
/remind me in 4 days
and then 4 days later a Todo is created for me.