Webhook support

[arthurka-o]

Hi 👋
I needed a Twitch EventSub for my Rails app, so I decided to add webhook support for this gem.
It needs much more work, but it works for my case already.

My controller looks something like this and initializer something like this

It was my first time working on a Ruby gem (with a help of LLM), so there're probably (surely) some strange things.

From what I see already:

• I imported ActiveSupport for a webhook handler, not a very nice thing for a ruby gem not related to Rails.
• Tests
• Probably good thing would be adding all possible even types and their conditions with returning data schemes
• Squashing commits

I would need an advice of someone more experienced with Ruby gems to finish this