Feat: Add insert variable icon in the header of prompt editor. #4764 (#5142)

### What problem does this PR solve?

Feat: Add insert variable icon in the header of prompt editor. #4764

### Type of change


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

web/src/locales/en.ts

@@ -1179,6 +1179,7 @@ This delimiter is used to split the input text into several text pieces echo of
       addCategory: 'Add category',
       categoryName: 'Category name',
       nextStep: 'Next step',
+      insertVariableTip: `Enter / Insert variables`,
     },
     footer: {
       profile: 'All rights reserved @ React',