followed https://github.com/rhobs/observability-operator, and installed observability-operator 0.0.15 from console, then create MonitoringStack instance from console, the "Create MonitoringStack" page, set replicas to negative value for prometheusConfig, such as -1, there is not error message to show the value is invalid

Version-Release number of selected component (if applicable):

observability-operator 0.0.15

How reproducible:

always

Steps to Reproduce:

1. see the description
2.
3.

Actual results:

there is not error message to show the value is invalid

Expected results:

should have error message