Cloned from https://bugzilla.redhat.com/show_bug.cgi?id=1756991

Description of problem:
When creating a template with 2 inputs with the same name, the error "uninitialized constant #<Class:0x000000000b894c38>::NonUniqueInputsError" appears and the operation fails. No traceback in production.log. Failure is expected but it should be handled better: the message should be more user friendly and preferably, the check should be handled before submitting the form.

Version-Release number of selected component (if applicable):
Reproduced on Sat 6.6 snap 22.

How reproducible:
Deterministic

Steps to Reproduce:
1. Monitor -> Report Templates -> Create
2. Set name
3. Go to Inputs tab
4. Add input, name it "abc"
5. Add another input, name it "abc"
6. Submit

Actual results:
Error, operation failed

Expected results:
(Form not submittable because this is checked by Javascript before submission). Better error message.