HAI-1527 API for changing permissions (#391)

Add API for changing the permissions of hanke kayttajat.

Add audit logging for the updates.

Add a security scheme to the OpenAPI configuration. This enables the use
of the Swagger UI by copying over your bearer token. Reformat some
OpenAPI descriptions, since they were shown as code blocks. Add Swagger
UI authentication instructions to README, enable it for all relevant
controllers

Add database indices for hanke id in hanke_kayttaja and some for the
permissions table.

Add a feature flag for user management and stop creating users and tokens
when the feature is off.

README.md

@@ -49,8 +49,21 @@ See docker-compose.yml for details.
 
 ### Swagger UI
 
-Swagger UI (see https://springdoc.org/) and OpenAPI v3 description (JSON). Note though that the swagger
-setup can not currently support authentication, so can not test the actions with it.
+Swagger UI (see https://springdoc.org/) and OpenAPI v3 description (JSON). You
+can use the Swagger UI to send requests, if you copy your bearer token over from
+the browser. So,
+1. Log in to Haitaton.
+2. Open the Network tab from developer tools.
+3. Open e.g. Omat Hankkeet in Haitaton.
+4. From the backend request, copy the content of the Authorization header, that
+   comes after the Bearer keyword.
+5. In the Swagger UI of the same environment, open the Authorize dialog.
+6. Paste the bearer token.
+7. Send a request as a logged-in user.
+
+Authentication for the GDPR API is different from the other application, and
+it's not configured for the Swagger UI. GDPR API can be tested using the
+specialized tester, as detailed in [GDPR API section](#gdpr-api).
 
 Locally without Docker: