Issue Summary

When using a user picker in the request creation form on the customer portal, users with project Admininistrator role see a misleading "Add new customer" prompt.

Attempting to add a new customer results in an "invalid field value" error, causing confusion.

Steps to Reproduce

1. Create a custom field as a user-picker type.
2. Add newly created user picker to a request type
3. Go to request creation in customer portal as a user with project administrator role.
4. Type in a non existent user email address into the user-picker field, then observe the prompt to "add new customer". 

Expected Results

The user picker should not prompt the option to "Add new customer". Rather, it should only list the existing users setup in the user-picker filter.

This feature appears to make more sense when raising request on behalf of customer, but for projects that require user picker fields for other reasons, this can be misleading.

Side Note: A request to remove this option for Reporter fields has also been raised: https://jira.atlassian.com/browse/JSDSERVER-15472

Actual Results

If typing a non-existent user address, then the following error will appear. 

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available

Versions Tested

Please confirm all versions that have been tested for this issue, and indicate whether the tested version is affected or not affected, below: