[sso-avatars] Also use env var for minio container

From minio's documentation:
- MINIO_ACCESS_KEY and MINIO_SECRET_KEY are deprecated in lieu of
  MINIO_ROOT_USER and MINIO_ROOT_PASSWORD respectively
- In order to rotate secrets we only need to change
  MINIO_ROOT_{USER,PASSWORD}

Using this commit and the previous one affecting keycloak we can use
per-instance keys as opposed to the current state.
In order to achieve this, AVATARS_ACCESS_KEY and AVATARS_SECRET_KEY must
be set to the desired values.

The only guidelines as to how to generate ACCESS_KEY and SECRET_KEY are:

> Specify a unique, random, and long string for both the ACCESSKEY and
> SECRETKEY. Your organization may have specific internal or regulatory
> requirements around generating values for use with access or secret keys.

See:
- https://docs.min.io/minio/baremetal/reference/minio-server/minio-server.html#envvar.MINIO_ACCESS_KEY
- https://docs.min.io/minio/baremetal/security/minio-identity-management/user-management.html

dd-sso/docker-compose-parts/avatars.yml

@@ -28,11 +28,9 @@ services:
       - ${DATA_FOLDER}/avatars:/data
       - ${SRC_FOLDER}/avatars:/root/.minio
     environment:
-      - MINIO_ACCESS_KEY=AKIAIOSFODNN7EXAMPLE
-      - MINIO_SECRET_KEY=wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY
+      - MINIO_ROOT_USER=${AVATARS_ACCESS_KEY:-AKIAIOSFODNN7EXAMPLE}
+      - MINIO_ROOT_PASSWORD=${AVATARS_SECRET_KEY:-wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY}
     restart: unless-stopped
-    # depends_on:
-    #   - ${KEYCLOAK_DB_ADDR}
     command: "server /data"
     networks:
       - dd_net