Add missing Kotlin Observability examples

See gh-46775

Signed-off-by: Łukasz Jernaś <lukasz.jernas@allegro.com>

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/actuator/loggers/opentelemetry/OpenTelemetryAppenderInitializer.kt

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2012-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.actuator.loggers.opentelemetry
+
+import io.opentelemetry.api.OpenTelemetry
+import io.opentelemetry.instrumentation.logback.appender.v1_0.OpenTelemetryAppender
+import org.springframework.beans.factory.InitializingBean
+import org.springframework.stereotype.Component
+
+@Component
+class OpenTelemetryAppenderInitializer(
+	private val openTelemetry: OpenTelemetry
+) : InitializingBean {
+
+	override fun afterPropertiesSet() = OpenTelemetryAppender.install(openTelemetry)
+
+}

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/actuator/observability/MyCustomObservation.kt

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+/*
+ * Copyright 2012-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.actuator.observability
+
+import io.micrometer.observation.Observation
+import io.micrometer.observation.ObservationRegistry;
+
+import org.springframework.stereotype.Component
+
+@Component
+class MyCustomObservation(private val observationRegistry: ObservationRegistry) {
+
+	fun doSomething() {
+		Observation.createNotStarted("doSomething", observationRegistry)
+			.lowCardinalityKeyValue("locale", "en-US")
+			.highCardinalityKeyValue("userId", "42")
+			.observe {
+				// Execute business logic here
+			}
+	}
+
+}

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/actuator/observability/preventingobservations/MyObservationPredicate.kt

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+/*
+ * Copyright 2012-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.actuator.observability.preventingobservations
+
+import io.micrometer.observation.Observation.Context
+import io.micrometer.observation.ObservationPredicate
+import org.springframework.stereotype.Component
+
+@Component
+class MyObservationPredicate : ObservationPredicate {
+
+	override fun test(name: String, context: Context): Boolean {
+		return !name.contains("denied")
+	}
+
+}