[JIRAALIGN-1285] Portfolio names can be modified to an existing portfolio name.

Issue Summary

Users are able to modify a portfolio name that already exists.

Steps to Reproduce

1. Go to Administration > Portfolio
2. Click Add Portfolio and set the necessary details and save.
3. Open the newly created portfolio and modify the name to a portfolio that already exists.

Expected Results

User should not be able to edit the portfolio name to a name of an existing portfolio.

Actual Results

User is able to successfully modify the portfolio name to a name of an existing portfolio.

Workaround

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