feature: add system setting service (#12408)

### What problem does this PR solve?

#12409 

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

admin/server/routes.py

@@ -21,7 +21,7 @@ from flask_login import current_user, login_required, logout_user
 
 from auth import login_verify, login_admin, check_admin_auth
 from responses import success_response, error_response
-from services import UserMgr, ServiceMgr, UserServiceMgr
+from services import UserMgr, ServiceMgr, UserServiceMgr, SettingsMgr
 from roles import RoleMgr
 from api.common.exceptions import AdminException
 from common.versions import get_ragflow_version
@@ -406,6 +406,49 @@ def get_user_permission(user_name: str):
     except Exception as e:
         return error_response(str(e), 500)
 
+@admin_bp.route('/variables', methods=['PUT'])
+@login_required
+@check_admin_auth
+def set_variable():
+    try:
+        data = request.get_json()
+        if not data and 'var_name' not in data:
+            return error_response("Var name is required", 400)
+
+        if 'var_value' not in data:
+            return error_response("Var value is required", 400)
+        var_name: str = data['var_name']
+        var_value: str = data['var_value']
+
+        SettingsMgr.update_by_name(var_name, var_value)
+        return success_response(None, "Set variable successfully")
+    except AdminException as e:
+        return error_response(str(e), 400)
+    except Exception as e:
+        return error_response(str(e), 500)
+
+@admin_bp.route('/variables', methods=['GET'])
+@login_required
+@check_admin_auth
+def get_variable():
+    try:
+        if request.content_length is None or request.content_length == 0:
+            # list variables
+            res = list(SettingsMgr.get_all())
+            return success_response(res)
+
+        # get var
+        data = request.get_json()
+        if not data and 'var_name' not in data:
+            return error_response("Var name is required", 400)
+        var_name: str = data['var_name']
+        res = SettingsMgr.get_by_name(var_name)
+        return success_response(res)
+    except AdminException as e:
+        return error_response(str(e), 400)
+    except Exception as e:
+        return error_response(str(e), 500)
+
 @admin_bp.route('/version', methods=['GET'])
 @login_required
 @check_admin_auth