Add migration for image verifiers

[KCSesh]

Related:
bottlerocket-os/bottlerocket-settings-sdk#114
bottlerocket-os/bottlerocket-core-kit#820
bottlerocket-os/bottlerocket-core-kit#841
#4766

Description of changes:

• Added a migration for the expansion of image-verifiers.

Testing done:

• Launched an old ami, and setup notation settings.
• Migrated to new AMI, and added a custom image verifier settings (only via setting - no bootstrap copy).
• Rolled back to old ami, and verified only notation settings were persisted.

Details

1.55.0

bash-5.2# apiclient get settings.image-verifier-plugins
{
  "settings": {
    "image-verifier-plugins": {
      "enabled": true,
      "notation": {
        "trustpolicy": "ewogICJ2ZXJzaW9uIjogIjEuMCIsCiAgInRydXN0UG9saWNpZXMiOiBbXQp9"
      }
    }
  }
}
bash-5.2# apiclient set settings.image-verifier-plugins.digestion.trustpolicy="ewogICJ2ZXJzaW9uIjogIjEuMCIsCiAgInRydXN0UG9saWNpZXMiOiBbXQp9"
Failed to change settings: Failed PATCH request to '/settings/keypair?tx=apiclient-set-Q8I8TyFmNICanHqu': Status 400 when PATCHing /settings/keypair?tx=apiclient-set-Q8I8TyFmNICanHqu: Unable to match your input to the data model.  We may not have enough type information.  Please try the --json input form.  Cause: Error during deserialization: unknown field `digestion`, expected `enabled` or `notation` at line 1 column 38

Move to 1.56.0

bash-5.2# apiclient get settings.image-verifier-plugins
{
  "settings": {
    "image-verifier-plugins": {
      "enabled": true,
      "notation": {
        "trustpolicy": "ewogICJ2ZXJzaW9uIjogIjEuMCIsCiAgInRydXN0UG9saWNpZXMiOiBbXQp9"
      }
    }
  }
}
bash-5.2# apiclient set settings.image-verifier-plugins.digestion.trustpolicy="ewogICJ2ZXJzaW9uIjogIjEuMCIsCiAgInRydXN0UG9saWNpZXMiOiBbXQp9"
bash-5.2# apiclient get settings.image-verifier-plugins
{
  "settings": {
    "image-verifier-plugins": {
      "digestion": {
        "trustpolicy": "ewogICJ2ZXJzaW9uIjogIjEuMCIsCiAgInRydXN0UG9saWNpZXMiOiBbXQp9"
      },
      "enabled": true,
      "notation": {
        "trustpolicy": "ewogICJ2ZXJzaW9uIjogIjEuMCIsCiAgInRydXN0UG9saWNpZXMiOiBbXQp9"
      }
    }
  }
}

Rollback to 1.55:

[ssm-user@control]$ apiclient get settings.image-verifier-plugins
{
  "settings": {
    "image-verifier-plugins": {
      "enabled": true,
      "notation": {
        "trustpolicy": "ewogICJ2ZXJzaW9uIjogIjEuMCIsCiAgInRydXN0UG9saWNpZXMiOiBbXQp9"
      }
    }
  }
}

**Terms of contribution:**

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.