[ci.jenkins.io] Enable disk backup for datadisk

[dduportal]

The goal is to ensure we have a daily backup of the JENKINS_HOME of ci.jenkins.io

Azure provides a Backup System, than can be used specifically for managed disks such as this one: https://learn.microsoft.com/en-us/azure/backup/backup-managed-disks.

We don't (and should not) need a VM-level backup as we use Puppet to manage the system: disaster recovery for ci.jenkins.io is to install a blank new VM and mount the resotre of the datadisk for Jenkins.

As per https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/data_protection_backup_instance_disk, we can define this using Terraform which implies importing ci.jenkins.io VM once for all.

A word about encryption:

• The backup vault is, like the VM disks, encrypted at rest with an Azure PMK key (hardware level).
• We can keep this behavior (encryption at rest with PMK) for the backup, as ci.jenkins.io deos not have any senstivie data (eventually credentials for GH org, but that is all).
• Note: This encryption could be provided a custom key private for sensitvie backups such as trusted.ci's

[dduportal]

Delaying this issue to another milestone:

• [ci.jenkins.io] Use a new VM instance type #3535 will introduce a new data disk will less data (since [ci.jenkins.io] Use Artifact Manager to store archived artifacts (and stashes) #3496 is applied)
• [ci.jenkins.io] Remove the plugin "JobConfigHistory" #3528 (comment)

[dduportal]

Closing as superseeded by #3535