Bug 1912907

Description of problem:

The HelmchartRepositories resource proxies a repositories' index.yaml file as-is. Some Helm repositories (e.g. Nexus3) generate index files containing relative chart URL's. These relative URL's - without base uri - are unreachable while instantiating helm charts.

Version-Release number of selected component (if applicable): 4.6


How reproducible:

prerequisite: OCP4 (v4.6) cluster and OC (Client Version: 4.6.8) + helm (Version:"v3.4.2") client available

Steps to Reproduce:
1. setup a nexus3:
~~~
$ helm repo add sonatype https://sonatype.github.io/helm3-charts/
$ helm install my-nexus-repository-manager sonatype/nexus-repository-manager --version 29.0.1 --set persistence.enabled=false --set nexus.securityContext=""
$ oc expose svc my-nexus-repository-manager
~~~ 
2. create helm repo:
~~~
$ curl -u admin:$(oc exec deployment/my-nexus-repository-manager -- cat /nexus-data/admin.password) -X POST "$(oc get route my-nexus-repository-manager  -o jsonpath='{.spec.host}')/service/rest/v1/repositories/helm/hosted" -H  "accept: application/json" -H  "Content-Type: application/json" -d "{  \"name\": \"helmtest\",  \"online\": true,  \"storage\": {    \"blobStoreName\": \"default\",    \"strictContentTypeValidation\": true,    \"writePolicy\": \"allow_once\"  },  \"cleanup\": {    \"policyNames\": [      \"string\"    ]  }}"
~~~
3. upload content:
~~~
$ curl https://charts.mirantis.com/charts/nginx-0.1.0.tgz -o nginx-0.1.0.tgz
$ curl -u admin:$(oc exec deployment/my-nexus-repository-manager -- cat /nexus-data/admin.password) "$(oc get route my-nexus-repository-manager  -o jsonpath='{.spec.host}')/repository/helmtest/" --upload-file nginx-0.1.0.tgz -v
~~~
4. create helmchartrepository:
~~~
$ cat <<EOF| oc apply -f -
apiVersion: helm.openshift.io/v1beta1
kind: HelmChartRepository
metadata:
  name: nexus
spec:
  connectionConfig:
    url: "http://$(oc get routes.route.openshift.io  my-nexus-repository-manager -o jsonpath='{.spec.host}')/repository/helmtest"
EOF
~~~
5. login to developer console and try to install the helm chart
[Developer Console] -> Add -> Helm Chart -> Nginx v0.1.0

Actual results:

While trying to install a release from the Helm chart in the Dashboard, the following error is shown:
~~~
Danger alert:Helm Chart cannot be installed
The Helm Chart is currently unavailable. Error: Failed to retrieve chart: failed to download "nginx-0.1.0.tgz" (hint: running `helm repo update` may help)
~~~
Expected results:

Helm chart installed

Additional info: