fix: handle nil annotations in mse.lua

Previously, mse.lua directly assigned obj.annotations to the annotations
variable without checking for nil, which would cause a runtime error when
the ingress object has no annotations. This aligns mse.lua with the
nil-guard pattern already used in higress.lua, nginx.lua, and aliyun-alb.lua.

Fixes #228

Author: anujagrawal380

lua_configuration/trafficrouting_ingress/mse.lua

@@ -4,7 +4,11 @@ function split(input, delimiter)
     return arr
 end
 
-annotations = obj.annotations
+annotations = {}
+if ( obj.annotations )
+then
+    annotations = obj.annotations
+end
 annotations["nginx.ingress.kubernetes.io/canary"] = "true"
 annotations["nginx.ingress.kubernetes.io/canary-by-cookie"] = nil
 annotations["nginx.ingress.kubernetes.io/canary-by-header"] = nil