Update azure-pipelines.yml with agency-specific variables

[thekaveman]

From the Terraform init task in azure-pipelines.yml:

- task: TerraformTaskV3@3
  displayName: Terraform init
  inputs:
    provider: azurerm
    command: init
    workingDirectory: "$(System.DefaultWorkingDirectory)/terraform"
    # https://developer.hashicorp.com/terraform/tutorials/automation/automate-terraform#automated-terraform-cli-workflow
    commandOptions: -input=false
    # service connection
    backendServiceArm: deployer
    # needs to match main.tf
    backendAzureRmResourceGroupName: courtesy-cards-eligibility-terraform
    backendAzureRmStorageAccountName: courtesycardsterraform
    backendAzureRmContainerName: tfstate
    backendAzureRmKey: terraform.tfstate

We need to variablize the following inputs:

• backendAzureRmResourceGroupName: courtesy-cards-eligibility-terraform
• backendAzureRmStorageAccountName: courtesycardsterraform

While keeping the above comment in mind:

# needs to match main.tf

See #292

Additional context

Will be impacted by the work from #284, but ideally here we don't care about how the pipeline is triggered, just where the input values come from.