Add support for AzureKeyVault@1 task

[samsmithnz]

• 1 failure on 7-Jan-2021

Azure DevOps docs: https://docs.microsoft.com/en-us/azure/devops/pipelines/tasks/deploy/azure-key-vault?view=azure-devops

# Azure Key Vault
# Download Azure Key Vault secrets
- task: AzureKeyVault@1
  inputs:
    azureSubscription: 
    keyVaultName: 
    secretsFilter: '*'
    runAsPreJob: false # Azure DevOps Services only

The to should probably just use Azure CLI at this stage (requiring an Azure login)