Enhance [p]info with a custom image.

### What component of Red (cog, command, API) would you like to see improvements on?

Core

### Describe the enhancement you're suggesting.

The following patch:
https://github.com/Cog-Creators/Red-DiscordBot/compare/V3/develop...DJTOMATO:Red-DiscordBot:patch-2

- Adds ``[p]set bot infoimage`` command which adds an image to [p]info command when using embeds
- Won't display if embeds are disabled.
- Defines ``infoimage`` as default variable.

### Anything else?

Hi, I'd like to hear org opinion on enhancing info command allowing end-users to further customize the bot with a custom image on the info page.