Set Log level by env (#3798)

### What problem does this PR solve?

Set Log level by env

### Type of change

- [x] Refactoring

docker/.env

@@ -129,3 +129,11 @@ TIMEZONE='Asia/Shanghai'
 # You can uncomment this line and update the value if you wish to change the 128M file size limit
 # MAX_CONTENT_LENGTH=134217728
 
+# The log level for the RAGFlow's owned packages and imported packages.
+# Available level:
+# - `DEBUG`
+# - `INFO` (default)
+# - `WARNING`
+# - `ERROR`
+# For example, following line changes the log level of `ragflow.es_conn` to `DEBUG`:
+# LOG_LEVELS=ragflow.es_conn=DEBUG