Make resource-detector compatible with Java 8 (#275)

Author: psx95

detectors/resources/build.gradle

@@ -15,6 +15,12 @@
  */
 description = 'Google Cloud resource provider for OpenTelemetry'
 
+afterEvaluate {
+	tasks.named("compileJava"){
+		options.release = 8
+	}
+}
+
 dependencies {
 	implementation(libraries.opentelemetry_api)
 	implementation(libraries.opentelemetry_sdk)