Support "subscription" events

[EL-JAYY]

General Troubleshooting

• I have checked for similar issues on the Issue-tracker.
• I have updated to the latest JDA version
• I have checked the branches or the maintainers' PRs for upcoming features.

Feature Request

JDA should imlement Wrappers for the Subscriptions Gateway Events, such as other API Wrappers have.

https://discord.com/developers/docs/events/gateway-events#subscriptions

Example Use-Case