Update AAI Tutorial, generalize for all cloud services
The AAI tutorial https://hifis.net/aai/howto has been acknowledged several times as helpful ... for indico, but somewhat misleading if user wants to use another service.
- Adapt the text and pics such that it can be understood as general instruction for all service
- Renew the date to make it appear on the posts list again
- mark with "updated", "changelog"
- add corresponding forwardings
- Remove the distinction into association and cloud services (beta) as this is not relevant in this context