feat: extended filters, fixed JSON format and added representation option

[sr258]

I've extended the plugin a bit:

• I've added a whitelist feature that allows you to filter by event type. (Currently there's only a blacklist)
• I've renamed "events" to "user events" and "admin operation" to "admin event" (these are the names in the KeyCloak UI)
• You can filter events by their resource paths (e.g. only get operations on users).
• The HTTP call produced invalid JSON, as it used ' and not ". I've fixed this.
• You can set an option so that the HTTP calls include the "representation" of events, e.g. a data structure with the user profile when the "UPDATE" admin event is triggered.
• I've updated the README configuration section so that it works with KeyCloak 17 and above.

[sr258]

I also updated the KeyCloak dependency to v20.0.2 as they added events to the enum and you can't filter for them if the dependency is not up-to-date.