chore(deps): bump org.testcontainers:testcontainers-bom in /backend

Bumps [org.testcontainers:testcontainers-bom](https://github.com/testcontainers/testcontainers-java) from 1.21.3 to 2.0.3.
- [Release notes](https://github.com/testcontainers/testcontainers-java/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-java/blob/main/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-java@1.21.3...2.0.3)

---
updated-dependencies:
- dependency-name: org.testcontainers:testcontainers-bom
  dependency-version: 2.0.3
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

backend/build.gradle

@@ -34,7 +34,7 @@ dependencies {
 	testImplementation 'io.projectreactor:reactor-test' // Add this for StepVerifier
 
 	// Test containers
-	testImplementation platform('org.testcontainers:testcontainers-bom:1.21.4')
+	testImplementation platform('org.testcontainers:testcontainers-bom:2.0.4')
 	testImplementation 'org.testcontainers:junit-jupiter'
 	testImplementation 'org.testcontainers:mongodb'
 	// end::tests[]