🔧(docker) fix prosody table creation on startup

Starting with PostreSQL 15, the CREATE privilege on public schema is revoked
from all users except the database owner.
Adding a connection to the Prosody database at container startup to manually
grant all privileges on the `public` schema, ensuring Prosody can create its
tables properly.

Author: wilbrdt

docker/files/docker-entrypoint-initdb.d/init_user_db.sh

@@ -6,3 +6,9 @@ psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" --dbname "$POSTGRES_DB" <<-E
     CREATE DATABASE prosody;
     GRANT ALL PRIVILEGES ON DATABASE prosody TO prosody;
 EOSQL
+
+# Connect to the prosody database to grant all privileges on schema public
+# Required since PostgreSQL > 15
+psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" --dbname "prosody" <<-EOSQL
+  GRANT ALL ON SCHEMA public TO prosody;
+EOSQL