fix: improve database configuration and healthchecks

- Enhance database connection checks in entrypoint.sh
Ref: docker/entrypoint.sh (lines 6-24)

- Standardize database environment variables
Ref: docker-compose.yaml (lines 34-38, 331-334)

- Update healthcheck configurations for better reliability
Ref: docker-compose.yaml (lines 337-341)
Ref: docker-compose.middleware.yaml (lines 22-26)

- Add proper network configuration
Ref: docker-compose.yaml (lines 329-330)

- Update database configuration documentation
Ref: middleware.env.example (lines 4-41)

docker/entrypoint.sh

@@ -5,7 +5,12 @@ echo "Starting Dify services..."
 
 # Enhanced database connection check
 check_postgres() {
-    pg_isready -h "${DB_HOST}" -p "${DB_PORT}" -U "${DB_USERNAME}" > /dev/null 2>&1
+    echo "Checking PostgreSQL connection to ${DB_HOST}:${DB_PORT}..."
+    pg_isready \
+        -h "${DB_HOST}" \
+        -p "${DB_PORT}" \
+        -U "${DB_USERNAME}" \
+        -d "${DB_DATABASE}"
 }
 
 check_redis() {