Update custom field value: add option for [Once] or [Always]

Hi Team,

I would like to propose an enhancement to the rules engine—specifically, the ability to control how frequently a Conversation custom field is updated.

It would be helpful to have a variable or condition that lets us specify whether a custom field should be updated only once or multiple times during a conversation. This is similar to the functionality we currently have when configuring auto-replies.

This flexibility would allow for more precise workflows and avoid unnecessary or repetitive updates, inflated logs, or unintended automation behavior. In many cases, we only need to set a custom field once as a flag or marker, and updating it multiple times can add noise or cause downstream issues in integrations and reporting.