Update CA handbook
- Removes redundant CA Support onboarding items
- Adds
Art of Community by Jono Bacon
as an onboarding step - Fixes minor mistakes (channel names, references to the support issue tracker)
Edited by Matija Čupić
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Art of Community by Jono Bacon
as an onboarding step