[Feature](json) Support json_search function (apache#40948)

Like mysql, json_search returns the path which point to a json string
witch match the pattern.
`SELECT JSON_SEARCH('["A",[{"B":"1"}],{"C":"AB"},{"D":"BC"}]', 'one',
'A_') as res;`
```
+----------+
| res      |
+----------+
| "$[2].C" |
+----------+
```

be/src/util/jsonb_document.h

@@ -345,6 +345,22 @@ struct leg_info {
 
     ///type: 0 is member 1 is array
     unsigned int type;
+
+    bool to_string(std::string* str) const {
+        if (type == MEMBER_CODE) {
+            str->push_back(BEGIN_MEMBER);
+            str->append(leg_ptr, leg_len);
+            return true;
+        } else if (type == ARRAY_CODE) {
+            str->push_back(BEGIN_ARRAY);
+            std::string int_str = std::to_string(array_index);
+            str->append(int_str);
+            str->push_back(END_ARRAY);
+            return true;
+        } else {
+            return false;
+        }
+    }
 };
 
 class JsonbPath {
@@ -362,6 +378,19 @@ class JsonbPath {
         leg_vector.emplace_back(leg.release());
     }
 
+    void pop_leg_from_leg_vector() { leg_vector.pop_back(); }
+
+    bool to_string(std::string* res) const {
+        res->push_back(SCOPE);
+        for (const auto& leg : leg_vector) {
+            auto valid = leg->to_string(res);
+            if (!valid) {
+                return false;
+            }
+        }
+        return true;
+    }
+
     size_t get_leg_vector_size() { return leg_vector.size(); }
 
     leg_info* get_leg_from_leg_vector(size_t i) { return leg_vector[i].get(); }