add support for prefixed commands

[noiverre]

Is your feature request related to a problem? Please describe.
give access to prefixed commands for certain roles and/or in certain channels or category

Describe the solution you'd like
add slash command to register and delete prefixed commands
define the cmd name with cmd parameter on the slash command
define the text content using text parameter on the slash command

usage flow:
/createtext cmd:hsr!speed text:https://pretend-this-is-a-hsr-speed-image-table.png
/deletetext cmd:hsr!speed

the bot will read message create event and if the 1st word match any prefixed command, bot will send the text content to the chat in that channel or category

role checks aren't necessary

Describe alternatives you've considered
use yagpdb

Additional context

[Iqrar99]

Sounds interesting. I actually had a planning about invoking custom command long time ago