Changelog: Skip some duplicated jobs

[sbrunner]

• The process should be uniformed for all kinds of events
• The discussion should be prioritized to be transformed in standard events
• The sub event should work
• With pull request, milestones and discussions, the old and new values should be taken in account

[sentry-io]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ ProgrammingError: (psycopg2.errors.UndefinedFunction) operator does not exist: json = json webhook View Issue
• ‼️ AttributeError: 'NoneType' object has no attribute 'get' webhook View Issue

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