Azure secret reference refactoring and enhancement

[ytsarev]

• Explicitly mention azure control variables in the values.yaml for proper visibility and documentation
• Scope the azure credentials related values under azuredns.createAuthSecret.*
• Bring up the Azure public DNS doc to README/website frontpage
• Enhance make deploy-full-local-setup with ability to deploy test k8gb chart and k8gb controller versions
• Update value examples in the Azure tutorial
• Fix newline control in -}} templating function to create properly formatted secret
• Fixes Azure DNS: ability to reference existing secret #1585

All changes tested e2e locally:

• The azure external secret is getting created with:

azuredns:
  # -- Enable Azure DNS provider
  enabled: true
  # -- Azure tenant ID which holds the managed identity
  createAuthSecret:
    enabled: true
    tenantId: myTenantID
    # -- subscription id which holds the Azure DNS zone
    subscriptionId: mySubscriptionID
    # -- Azure Resource Group which holds the Azure DNS Zone (which is defined as 'edgeDNSZone')
    resourceGroup: k8gb-kubeconeu2023
    aadClientId: myAADClientID
    aadClientSecret: myAADClientSecret

k view-secret -n k8gb external-dns-secret-azure
Choosing key: azure.json
{
  "tenantId": "myTenantID",
  "subscriptionId": "mySubscriptionID",
  "resourceGroup": "k8gb-kubeconeu2023",
  "aadClientId": "myAADClientID",
  "aadClientSecret": "myAADClientSecret",
  "useManagedIdentityExtension": false,
  "userAssignedIdentityID": "myUserAssignedIdentityID",
  "useWorkloadIdentityExtension": false
}

In case of

azuredns:
  # -- Enable Azure DNS provider
  enabled: true
  authSecretName: external-dns-secret-azure-test
  # -- Azure tenant ID which holds the managed identity
  createAuthSecret:
    enabled: false

The external-dns-secret-azure-test was created separately from the helm chart installation and was properly picked up by extenral-dns deployment.

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