Performance Max Upgrade status enum for campaign.

[Proto definition ![GitHub](https://developers.google.com/site-assets/logo-github.svg)](https://github.com/googleapis/googleapis/blob/master/google/ads/googleads/v26/enums/performance_max_upgrade_status.proto)

| Enums ||
|---|---|
| ## `UNKNOWN` | Used for return value only. Represents value unknown in this version. |
| ## `UNSPECIFIED` | Not specified. |
| ## `UPGRADE_COMPLETE` | The upgrade to a Performance Max campaign is complete. |
| ## `UPGRADE_ELIGIBLE` | The campaign is eligible for upgrade to a Performance Max campaign. |
| ## `UPGRADE_FAILED` | The upgrade to a Performance Max campaign failed. The campaign will still serve as it was before upgrade was attempted. |
| ## `UPGRADE_IN_PROGRESS` | The upgrade to a Performance Max campaign is in progress. |