chore: use logging.getLevelNamesMapping()

Use `logging.getLevelNamesMapping()` for getting all valid logging levels. This also allows adding new ones using `logging.addLevel()`. This feature was [added](https://docs.python.org/3.11/library/logging.html#logging.getLevelNamesMapping) in Python 3.11 which is above the minimum supported Python version for open-webui.

backend/open_webui/env.py

@@ -65,10 +65,8 @@ except Exception:
 # LOGGING
 ####################################
 
-log_levels = ["CRITICAL", "ERROR", "WARNING", "INFO", "DEBUG"]
-
 GLOBAL_LOG_LEVEL = os.environ.get("GLOBAL_LOG_LEVEL", "").upper()
-if GLOBAL_LOG_LEVEL in log_levels:
+if GLOBAL_LOG_LEVEL in logging.getLevelNamesMapping():
     logging.basicConfig(stream=sys.stdout, level=GLOBAL_LOG_LEVEL, force=True)
 else:
     GLOBAL_LOG_LEVEL = "INFO"
@@ -100,7 +98,7 @@ SRC_LOG_LEVELS = {}
 for source in log_sources:
     log_env_var = source + "_LOG_LEVEL"
     SRC_LOG_LEVELS[source] = os.environ.get(log_env_var, "").upper()
-    if SRC_LOG_LEVELS[source] not in log_levels:
+    if SRC_LOG_LEVELS[source] not in logging.getLevelNamesMapping():
         SRC_LOG_LEVELS[source] = GLOBAL_LOG_LEVEL
     log.info(f"{log_env_var}: {SRC_LOG_LEVELS[source]}")