Update docker-compose.yml & documentation

• docker-compose.yml: Reorder environment variables lexicographically & add a new one for the http path
• Documentation update to reflect keycloak v17+
• Additionally, this MR aims to deploy keycloak to v18 (set through the CI variables)

Note: As Keycloak from v17+ has stripped the default /auth from its URLs, we offer the possibility to redefine it in an env variable. This comes in handy when many clients still use the old URL and thus saves effort from manually updating these URLs.

assigned to @sotirios.tsepelakis

changed the description

added documentation migration labels

merged