chore(deps): bump com.squareup.okhttp3:okhttp in /backend

Bumps [com.squareup.okhttp3:okhttp](https://github.com/square/okhttp) from 4.11.0 to 5.2.1.
- [Changelog](https://github.com/square/okhttp/blob/master/CHANGELOG.md)
- [Commits](square/okhttp@parent-4.11.0...parent-5.2.1)

---
updated-dependencies:
- dependency-name: com.squareup.okhttp3:okhttp
  dependency-version: 5.2.1
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

backend/pom.xml

@@ -281,7 +281,7 @@
         <dependency>
             <groupId>com.squareup.okhttp3</groupId>
             <artifactId>okhttp</artifactId>
-            <version>4.11.0</version>
+            <version>5.2.1</version>
         </dependency>
 
         <!--        gRPC implementation-->