Leftover from api-platform 3.0 upgrade (#3176)

Summary bucket of leftovers from PR #3176

- [x] Review changes done in https://github.com/api-platform/api-platform and take over what makes sense #3255 #3304
- [ ] Review if we want to support multiple ApiResources in our various extensions (UriTemplateFactory, etc.)
- [ ] Plural naming for /reset_password endpoint
- [ ] Test coverage for data providers
- [ ] Invitation endpoint: align more closely to REST principle
- remove /find from GET operation
- evaluate DELETE instead of PATCH (not sure this is correct, though)
- [ ] re-evaluate metadata cache and check if additional configuration in services.yaml could be safely removed
(related to https://github.com/api-platform/core/issues/5285 and https://github.com/api-platform/core/issues/4975)