Add Kotlin main artifacts to dependency management

This commit adds Kotlin main artifacts to Spring
Boot dependency management and will be replaced by
Kotlin BOM when it will be available (see KT-18398).

See gh-9486

spring-boot-project/spring-boot-dependencies/pom.xml

@@ -107,6 +107,7 @@
 		<junit.version>4.12</junit.version>
 		<junit-jupiter.version>5.0.1</junit-jupiter.version>
 		<junit-platform.version>1.0.1</junit-platform.version>
+		<kotlin.version>1.1.51</kotlin.version>
 		<lettuce.version>5.0.0.RELEASE</lettuce.version>
 		<liquibase.version>3.5.3</liquibase.version>
 		<log4j2.version>2.9.1</log4j2.version>
@@ -2264,6 +2265,26 @@
 				<artifactId>jooq-codegen</artifactId>
 				<version>${jooq.version}</version>
 			</dependency>
+			<dependency>
+				<groupId>org.jetbrains.kotlin</groupId>
+				<artifactId>kotlin-reflect</artifactId>
+				<version>${kotlin.version}</version>
+			</dependency>
+			<dependency>
+				<groupId>org.jetbrains.kotlin</groupId>
+				<artifactId>kotlin-stdlib</artifactId>
+				<version>${kotlin.version}</version>
+			</dependency>
+			<dependency>
+				<groupId>org.jetbrains.kotlin</groupId>
+				<artifactId>kotlin-stdlib-jre7</artifactId>
+				<version>${kotlin.version}</version>
+			</dependency>
+			<dependency>
+				<groupId>org.jetbrains.kotlin</groupId>
+				<artifactId>kotlin-stdlib-jre8</artifactId>
+				<version>${kotlin.version}</version>
+			</dependency>
 			<dependency>
 				<groupId>org.liquibase</groupId>
 				<artifactId>liquibase-core</artifactId>