It seems Oathkeeper is currently not able to NOT generate an ID token for anonymous users. Therefore, if the username == 'anonymous' a non-authenticated (aka anonymous) user is assumed.

This commit accepts JWT-based ID tokens generated from Oathkeeper acting as a reverse proxy in front of Okuna. In that setup Oathkeeper retrieves a session token, either via 'X-Session-Token' header (API authentication) or via a session cookie (Browser authentication), validates and converts it to a JWT-based Open ID connect compatible ID token. This ID token is then validated by Okuna. Users not existing, are auto-created by using the ID token 'sub' as username and 'email' as email.

- increases username length to 36 (i.e. the length of the Ory user UUID)
- makes name field in the user profile optional

HOLI-1411: update README

See merge request holisticfoundation/holi-okuna!4

NOISSUE: remove deprecation warnings via version bumps

See merge request holisticfoundation/holi-okuna!3

HOLI-1399: change database to postgres

See merge request holisticfoundation/holi-okuna!2

HOLI-1401: django version upgrade

See merge request holisticfoundation/holi-okuna!1

In order to make this work I had to work around things:

* psycopg2 > 2.9.0 is incompatible with Django 2.2, therefore used 2.8.6
  (see https://stackoverflow.com/a/68025007/1242529)
* migrations failed for a change from duration to datetime (with timezone). I modified migration
  history as we'll start with an empty DB anyways so fiddling with migration history shouldn't be
  an issue
* there was a duplicate constraint 'reporter_moderated_object_constraint' of which I renamed one
  to 'reporter_moderation_report_constraint'

To validate this MR locally, make sure you clean up your local env, e.g. by running:

```sh
python okuna-cli.py down-services-only
python okuna-cli.py clean
```

Then, stop any running docker containers related to Okuna. Subsequently, running

```
python okuna-cli.py up-services-only
```

should have Okuna start with an empty DB within postgres and successfully auto-applying migrations.

switch to MIT license

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