api-platform template upgrades

Potentially open points from PR #5123
(to be investigated individually)

- [ ] Worker mode (runtime mode)
- [x] Upgrade to postgres 16
- [ ] api platform config rfc_7807_compliant_errors (upstream is true; kept at false)
- [ ] doctrine config validate_xml_mapping (upstream is true; kept at false)
- [ ] upstream switched from phpdocumentor/reflection-docblock to phpstan/phpdoc-parser (this generated wrong API responses; didn't debug further)
- [ ] Some renaming of files to keep review of the changes a bit simpler. We could still do these renamings afterwards in a separate PR (docker-compose.yml is now compose.yml; api-platform.ini is now app.ini; etc.)