Add ability to edit existing Payload Variables in alerting

Why is this needed: Currently, when configuring a Custom Payload in alerting, it is not possible to edit existing Payload Variables. If you make a mistake or want to update a variable’s value, the only option is to delete it and re-add it. This makes the workflow slower and less convenient, especially when working with multiple variables. What would you like to be added: Add the ability to edit existing Payload Variables directly — for example, by providing an edit (pencil) button next to each variable. This would allow users to quickly modify variable values without having to remove and recreate them. Who is this feature for? This feature would be useful for anyone configuring alerting and templated payloads, especially users managing complex payloads with multiple variables. It improves usability and reduces configuration time. <img width="518" height="325" alt="Image" src="https://github.com/user-attachments/assets/07ef5ea0-d60a-4f64-8267-760a810e87c4" />