Fixing bootRun task (#9)

### What's done:
- fixing the task using a workaround springdoc/springdoc-openapi-gradle-plugin#121

Author: orchestr7

backend/build.gradle.kts

@@ -2,10 +2,19 @@ plugins {
     id("com.saveourtool.template.build.spring-boot-kotlin-configuration")
     id("com.saveourtool.template.build.s3-local-run-configuration")
     id("com.saveourtool.template.build.mysql-local-run-configuration")
+    application
+}
+
+application {
+  mainClass.set("com.saveourtool.template.backend.BackendApplicationKt")
 }
 
 kotlin {
-    jvm()
+    jvm {
+        // another workaround:
+        // https://stackoverflow.com/questions/69437212/how-to-use-gradle-distribution-plugin-alongside-with-kotlin-multiplatform
+        withJava()
+    }
 
     sourceSets {
         jvmMain {

gradle/plugins/src/main/kotlin/com/saveourtool/template/build/spring-boot-kotlin-configuration.gradle.kts

@@ -12,6 +12,11 @@ plugins {
     kotlin("plugin.serialization")
     id("org.springframework.boot")
     id("io.spring.dependency-management")
+    // • First project (Spring Boot 3.1.2, Gradle 8.1.1) was fixed by adding id("application") as first plugin. @nbam-e 's idea about moving Kotlin before Spring Boot also worked for me.
+    // • Second project (Spring Boot 2.7.14, Gradle 7.6.1) was fixed with same way as first project (by adding id("application")).
+    // • Third project (Spring Boot 2.7.14, Gradle 8.1.1) didn't work at all.
+    // Workaround from https://github.com/springdoc/springdoc-openapi-gradle-plugin/issues/121
+    application
 }
 
 @Suppress("GENERIC_VARIABLE_WRONG_DECLARATION")