Bump org.springframework.boot from 3.0.1 to 3.1.5 in /springboot-app

Bumps [org.springframework.boot](https://github.com/spring-projects/spring-boot) from 3.0.1 to 3.1.5.
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v3.0.1...v3.1.5)

---
updated-dependencies:
- dependency-name: org.springframework.boot
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

springboot-app/build.gradle.kts

@@ -1,5 +1,5 @@
 plugins {
-  id("org.springframework.boot") version "3.0.1"
+  id("org.springframework.boot") version "3.1.5"
   id("io.spring.dependency-management") version "1.1.0"
   kotlin("jvm") version "1.7.22"
   kotlin("plugin.spring") version "1.7.22"