[ILM] Invalid form when enabling rollover defaults

[alisonelizabeth]

Kibana version:
7.11

Describe the bug:
The ILM policy form sometimes incorrectly reports a form error when enabling rollover defaults.

Steps to reproduce:

1. Create a ILM policy with no rollover configuration.

PUT _ilm/policy/my_policy
{
  "policy": {
    "phases": {
      "hot": {
        "actions": {
          "unfollow" : {}
        }
      }
    }
  }
}

2. Navigate to the ILM UI and select the policy created in step 1 to edit.
3. Open Advanced Settings for the hot phase and enable "Enable rollover"
4. Enable "Use recommended values"
5. Save the policy. Note user is unable to save the policy due to form error.

Screenshots (if relevant):
It appears the form is not updated with the default rollover configuration values and validation fails.

[elasticmachine]

Pinging @elastic/es-ui (Team:Elasticsearch UI)

[alisonelizabeth]

This has been fixed as part of #87213.