Create webhook message parser and handlers

[JohanX]

Github sends webhook messages to the same endpoint but with different payloads.
The type of webhook events being sent can be customised when creating the webhook in the repository.
For the purpose of this project, the "projects_v2_item" type should be used.
Acceptance criteria:

• A parser and multiple handlers should be created, based on the message payload.
• Tests are added for these handlers.

[olie-chan]

@JohanX Does this need any of your work in #5?

[JohanX]

Yes, it actually depends on that item being finished and working.

[github-actions]

🎉 This issue has been resolved in version 1.0.1 🎉

The release is available on:

• GitHub release

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