feat(terraform: azure-jenkinsinfra-controller) allow DNS to use distinct provider or to be undefined

[dduportal]

Related to jenkins-infra/helpdesk#3913 (edited).

Migrating the controller VM to the new subscription will need instantiating the module azure-jenkinsinfra-controller (either a new one or the current one). This module takes care of creating not only the VM, but also DNS records to reach this VM. But as our DNS zones for the jenkins.io and jenkins-ci.org domains are NOT in the secondary (sponsored) subscription, it will be an obstacle.

As a remidation, this PR adds a new feature to the terraform module azure-jenkinsinfra-controller to allow DNS records:

• To be managed by a distinct AzureRM provider
• To NOT be managed

So we can handle many cases during the migration of ci.jenkins.io

Tested with success:

• Using a local terraform plan against the 3 existing controllers:

$ terraform plan --target=module.ci_jenkins_io -target=module.trusted_ci_jenkins_io -target=module.cert_ci_jenkins_io
# ...

No changes. Your infrastructure matches the configuration.

Terraform has compared your real infrastructure against your
configuration and found no differences, so no changes are needed.
╷
│ Warning: Resource targeting is in effect
# ...

• Using the local copy of feat(ci.jenkins.io) add a secondary (empty) VM to prepare moving controller to secondary sponsored subscription azure#583 (edited):

$ terraform plan --target=module.ci_jenkins_io -target=module.trusted_ci_jenkins_io -target=module.cert_ci_jenkins_io --target=module.ci_jenkins_io_sponsorship

# ...
Plan: 25 to add, 0 to change, 0 to destroy.
╷
│ Warning: Resource targeting is in effect