[FEATURE] Add HTTP-REST API for Events

[albig]

Requirements

Features

• [ ] fetch all events (exclude hidden, deleted)
• [x] fetch events by given contraints like categories, past, only-future, tbd.
• [ ] fetch events a given user has subscribed
• [ ] make the API disabled by default
• [ ] possibility to authenticate e.g. by token to deny access by others
• [ ] TYPO3 9.5 LTS and 10.4 LTS compatility

[albig]

Work is done in the develop branch.

[albig]

The branch itself works.

Open tasks / questions

• We should exclude the subscriber details in the event lists. Maybe even some more data.
• We absolutely need some access token which is not public. Otherwise users could have access to events / details what is not intended
• Without token and without further settings, no event should be returned IMHO.