Add App evaluationContext for Conditions and Validators#87

Currently, conditions and validations are executed in the current user’s context. Atlassian has (an experimental) option to select App context for Conditions and Validations:
https://developer.atlassian.com/cloud/jira/platform/modules/workflow-validator/
https://developer.atlassian.com/cloud/jira/platform/modules/workflow-condition/

Use case: validate user groups fails because current user is not an admin and doesn’t have access to user groups.