Add imagePlatform option for image building

An `imagePlatform` option for the Maven and Gradle image-building
goal/task can be used to specify the os/architecture of any
builder, run, and buildpack images that are pulled during image
building.

Closes gh-40944

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/tasks/bundling/BootBuildImageTests.java

@@ -31,6 +31,7 @@ import org.springframework.boot.buildpack.platform.build.BuildRequest;
 import org.springframework.boot.buildpack.platform.build.BuildpackReference;
 import org.springframework.boot.buildpack.platform.build.PullPolicy;
 import org.springframework.boot.buildpack.platform.docker.type.Binding;
+import org.springframework.boot.buildpack.platform.docker.type.ImagePlatform;
 import org.springframework.boot.buildpack.platform.docker.type.ImageReference;
 import org.springframework.boot.gradle.junit.GradleProjectBuilder;
 
@@ -324,4 +325,15 @@ class BootBuildImageTests {
 				"label=role:ROLE");
 	}
 
+	@Test
+	void whenImagePlatformIsNotConfiguredThenRequestHasNoImagePlatform() {
+		assertThat(this.buildImage.createRequest().getImagePlatform()).isNull();
+	}
+
+	@Test
+	void whenImagePlatformIsConfiguredThenRequestHasImagePlatform() {
+		this.buildImage.getImagePlatform().set("linux/arm64/v1");
+		assertThat(this.buildImage.createRequest().getImagePlatform()).isEqualTo(ImagePlatform.of("linux/arm64/v1"));
+	}
+
 }