[RFE] Add TypeScript Support

[mitchwadair]

Is your feature request related to a problem? Please describe. A lot of people might use TS to develop their applications.

Describe the solution you'd like TES should support that by providing type definitions for TES functions. This would be provided through DefinitelyTyped. Maintaining these types will probably be a bit of a pain as EventSub is updated, but not a huge deal. Some examples of things that would need to be added:

• Every subscription type
• Condition types for subscriptions
• Payloads
• Subscriptions
• etc

[mitchwadair]

Might be able to avoid publishing to DefinitelyTyped by just including a .d.ts file and adding the types key in package.json See: https://betterstack.dev/blog/publishing-type-definitions-with-npm-package/#heading-including-type-definitions