Allow preemptive authentication for helm proxy repositories

ISSUE:

Unable to retrieve helm chars from remote Artifactory repository.

CAUSE:

When nexus requests index.yaml file from remote Artifactory server, its not challenging with authenticate header and serves partial file.

$ curl  https://repos.prod.remote.cloud/artifactory/helm-customer/index.yaml
apiVersion: v1
generated: 2022-10-27T00:35:57.983468Z

Remote server expects preemptive authentication to serve full content of the index.yaml file, which nexus doesn't do even when its configured with basic authentication details.

EXPECTED BEHAVIOR:

Nexus allows preemptive authentication for helm proxy repository, similar to maven proxy repository.

CURRENT BEHAVIOR:

Helm clients unable to download charts from remote server via nexus proxy