Emit events when a shared API token is changed

[mikeshardmind]

Feature request

Select the type of feature you are requesting:

• Cog
• Command
• API functionality

Describe your requested feature

Should emit the name of the service which was updated. This will allow cogs to cache the values and only update when if they change.

[zephyrkul]

Doesn't config already use a cache? Also, would it be worth expanding the event scope to consider config changes overall?

[mikeshardmind]

Config doesn't cache for DB backends. This is one of the only places 3rd party code might be caching a setting in nonobvious way (such as a single aiohttp client session) and should receive an indication to update