There is no error message if the Preflight Check fails due to a Request Header larger than the Tomcat limit

Steps to reproduce:

1. Add a very large number of projects is included in the Preflight Checker validation, in a way that the resulting Request Header is larger than the Tomcat limit (see details here).
2. Click on Validate to run the Preflight Check.

Expected result:
The Preflight Checker should display an error message indicative of the problem, instructing the user to reduce the amount of projects included in the validation and try again.

Current behavior:
The validation will simply fail with an error 400 (see image below), without any further information allowing for the troubleshooting of the problem.