Add support for missing types of changes on the ProjectV2Item

We currently support changes in date fields (like start_date, end_date), and single choice fields (like status)

Would be great to add support for at least the following:

- [ ] #18
- [ ] #17
- [ ] #16


This can be added here: https://github.com/EuroPython/internal-bot/blob/main/intbot/core/integrations/github.py#L168-L199

And the tests for this are here: https://github.com/EuroPython/internal-bot/blob/main/intbot/tests/test_integrations/test_github.py#L182-L249

Would be also great to refactor that changes parsing code, but that could be something for later :)

The example of the webhooks with different types of data are in the comments.