Fix docker-compose dependency to match implementation plan

Change from developmentOnly(libs.spring.boot.docker.compose) to
implementation("org.springframework.boot:spring-boot-docker-compose")
as specified in the implementation plan for issue #60.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: kukv

examples/webflux/custom-provider-database/build.gradle.kts

@@ -8,5 +8,5 @@ dependencies {
     implementation(libs.spring.boot.starter.webflux)
     implementation("org.springframework.boot:spring-boot-starter-data-r2dbc")
     runtimeOnly("org.postgresql:r2dbc-postgresql")
-    developmentOnly(libs.spring.boot.docker.compose)
+    implementation("org.springframework.boot:spring-boot-docker-compose")
 }