Add ability to override block device mapping configurations for all devices

[jakauppila]

🙍 Problem Statement

To override configurations within block_device_mappings you need to call out each define and each configuration

block_device_mappings:
  - device_name: /dev/sda
    ebs:
      volume_size: 20
      delete_on_termination: true
  - device_name: /dev/sdb
    ebs:
      volume_type: gp2
      virtual_name: test
      volume_size: 15
      delete_on_termination: true
      snapshot_id: snap-0015d0bc

https://kitchen.ci/docs/drivers/aws/#disk-configuration

It would be great if we could override (or provide defaults) for all devices with a single configuration.

❔ Possible Solution

I'm not sure the best way to combine the configuration in this case, do we need a new block that can provide defaults when building the object?

block_device_mappings_defaults:
    ebs:
      volume_type: gp3
      volume_size: 8
      delete_on_termination: true

⤴️ Describe alternatives you've considered

➕ Additional context

I'd be happy to implement this change if there's agreement on how to define the configuration.