[BUGFIX] fix portName reference in ingress

[hairmare]

Description

We found the following error when trying to configure an Ingress using version 0.1.2 of the chart.

$ helm install perses perses/perses --set ingress.ingressClassName=nginx --set ingress.enabled=true
Error: INSTALLATION FAILED: 1 error occurred:
        * Ingress in version "v1" cannot be handled as a Ingress: json: cannot unmarshal number into Go struct field ServiceBackendPort.spec.rules.http.paths.backend.service.port.name of type string

This PR aims at fixing it by introducing service.portName.

Checklist

• Pull request has a descriptive title and context useful to a reviewer.
• Pull request title follows the [<catalog_entry>] <commit message> naming convention using one of the following catalog_entry values: FEATURE, ENHANCEMENT, BUGFIX, BREAKINGCHANGE, IGNORE.
• All commits have DCO signoffs.

[Nexucis]

oupsy oupsy. Thank you for fixing it !!