[ISSUE] add the issuer backend url to orchestration configmap - 8.8

[hamza-m-masood]

Describe the issue:

Currently, the orchestration cluster does not support the issuer backend URL. This is why the 8.8 Helm chart is only using the public issuer URL:

camunda-platform-helm/charts/camunda-platform-8.8/templates/orchestration/configmap.yaml

Lines 46 to 50 in 92583af

	{{/*
	TODO: Add "camundaPlatform.authIssuerBackendUrl" when "backend-url" config is supported by the Orchestration Identity.
	For more details: https://github.com/camunda/camunda-platform-helm/issues/3952
	*/}}
	issuer-uri: {{ (include "camundaPlatform.authIssuerUrl" .) | quote }}

When the orchestration cluster supports the issuer backend URL, it should be added to the orchestration cluster configmap in the Helm chart.

More details.