Add support for user-based smart values for DevOps automation triggers

Since we shipped the new devops automation triggers, we are beginning to see clamour from customers to add user-based smart values.

For example:

"We often have the scenario, that someone creates a pull request in bitbucket and adds a reviewer from our team to this pull request. Is there a way to use the pull request created trigger and automatically assign the corresponding JIRA issue to this reviewer?"

Would open up new power for users.

Example smart-values might be: