request: auto messages

[favna]

Is your feature request related to a problem? Please describe.

Multiple times now there has been a request for Skyra to be able to automatically send a message in a Guild channel on a specific schedule, for example every hour. Such messages could be used to remind people to subscribe / remind them about the rules / etc, whatever people want. It is something that is available in other moderation bots as well.

Describe the solution you'd like

automessage command that creates a schedule entry to automatically send the messages

Describe alternatives you've considered

N/a.

Additional context

https://discordapp.com/channels/254360814063058944/382531782387695616/784550693520277535

#207 in #suggestions.