Added md help files for REST connector

ui-ngx/src/assets/help/en_US/widget/lib/gateway/rest-json_fn.md

@@ -0,0 +1,53 @@
+### JSON Path:
+
+The expression field is used to extract data from the HTTP response message.
+
+JSONPath expressions specify the items within a JSON structure (which could be an object, array, or nested combination of both) that you want to access. These expressions can select elements from JSON data on specific criteria. Here's a basic overview of how JSONPath expressions are structured:
+
+- `$`: The root element of the JSON document;
+- `.`: Child operator used to select child elements. For example, $.store.book ;
+- `[]`: Child operator used to select child elements. $['store']['book'] accesses the book array within a store object;
+
+### Examples:
+
+For example, if we want to extract the device name from the following message, we can use the expression below:
+
+HTTP response message:
+
+```json
+{
+	"sensorModelInfo": {
+		"sensorName": "AM-123",
+		"sensorType": "myDeviceType"
+	},
+	"data": {
+		"temp": 12.2,
+		"hum": 56,
+		"status": "ok"
+	}
+}
+```
+
+Expression:
+
+`${sensorModelInfo.sensorName}`
+
+Converted data:
+
+`AM-123`
+
+If we want to extract all data from the message above, we can use the following expression:
+
+`${data}`
+
+Converted data:
+
+`{"temp": 12.2, "hum": 56, "status": "ok"}`
+
+Or if we want to extract specific data (for example “temperature”), you can use the following expression:
+
+`${data.temp}`
+
+And as a converted data we will get:
+
+`12.2`

ui-ngx/src/assets/help/en_US/widget/lib/gateway/rest-url_fn.md

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+## Request URL expression
+
+JSONPath expression uses for creating url address to send a message.
+
+JSONPath expressions specify the items within a JSON structure (which could be an object, array, or nested combination of both) that you want to access. These expressions can select elements from JSON data on specific criteria. Here's a basic overview of how JSONPath expressions are structured:
+
+- `$`: The root element of the JSON document;
+- `.`: Child operator used to select child elements. For example, $.store.book ;
+- `[]`: Child operator used to select child elements. $['store']['book'] accesses the book array within a store object;
+
+### Examples:
+
+For example, if we want to extract the device name from the following message, we can use the expression below:
+
+HTTP response message:
+
+```json
+{
+	"sensorModelInfo": {
+		"sensorName": "AM-123",
+		"sensorType": "myDeviceType"
+	},
+	"data": {
+		"temp": 12.2,
+		"hum": 56,
+		"status": "ok"
+	}
+}
+```
+
+Expression:
+
+`${sensorModelInfo.sensorName}`
+
+Converted data:
+
+`AM-123`
+
+If we want to extract all data from the message above, we can use the following expression:
+
+`${data}`
+
+Converted data:
+
+`{"temp": 12.2, "hum": 56, "status": "ok"}`
+
+Or if we want to extract specific data (for example “temperature”), you can use the following expression:
+
+`${data.temp}`
+
+And as a converted data we will get:
+
+`12.2`