[Task] dynamic Version 4 UUID creation

### Description

Hi Team,

Was wondering if there could be an option to add a functionality which provides the option to create random Version 4 UUID's which can then be used as part of the payload for the second Metric that could be created as documented here https://hertzbeat.apache.org/docs/advanced/extend-http-example-token.

### Task List

- Create a custom monitor
- Add the functionality like using a variable {{v4uuid}} as part of the "payload" dynamically and can be used on further metrics.

Start with the documented HTTP example at https://hertzbeat.apache.org/docs/advanced/extend-http-example-token and inspect how a custom monitor handles metric payloads. Trace whether a value created for one metric can be referenced by a later metric, and consider the task complete when a {{v4uuid}} variable produces a random Version 4 UUID in the subsequent payload.

Written by the indexing model from the issue text.