chore: bump plugin.spring from 1.9.23 to 2.0.0 in /backend (#188)

Bumps [plugin.spring](https://github.com/JetBrains/kotlin) from 1.9.23 to 2.0.0.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v2.0.0/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.9.23...v2.0.0)

---
updated-dependencies:
- dependency-name: plugin.spring
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

backend/build.gradle.kts

@@ -4,7 +4,7 @@ plugins {
     id("org.springframework.boot") version "3.2.5"
     id("io.spring.dependency-management") version "1.1.4"
     kotlin("jvm") version "1.9.23"
-    kotlin("plugin.spring") version "1.9.23"
+    kotlin("plugin.spring") version "2.0.0"
 
     id("com.netflix.dgs.codegen") version "6.2.1"