chore(adopters): add OneStream to adopters list (#165)

Author: cschmalzonestream

ADOPTERS.md

@@ -7,3 +7,4 @@ to gain momentum and credibility.
 | Organization                            | Description of Use                          |
 | --------------------------------------- | ------------------------------------------- |
 | [Dynatrace](https://www.dynatrace.com/) | Monitoring of services managed in Backstage |
+| [OneStream](https://www.onestream.com)  | Enhancing the developer experience by having a one-stop shop for seeing their applications and services and proactively gathering performance information such as error logs and quality gate validations.                |