API v2 get user profile

Implement endpoint `GET /api/v2/me` to get the user profile.

* [ ] return 200 in case of success
* [ ] return a field in case of success
* [ ] create method in the business layer
* [ ] check returned object is uniform with other endpoints
* [ ] remove `GET api/v2/auth/whoami`
* [ ] deprecate `GET /user/whoami`
* [ ] openapi: document endpoint
* [ ] openapi: deprecate `GET /user/whoami`