Add Kafka Streams samples

- Add `http-ingest` source application that adds function composition example
 - Move the KStream samples from SCSt samples and modify them for SCDF stream

Address review comments

 - Add depenency management BOM
 - Add README

kafka-samples/http-ingest/src/main/java/org/springframework/cloud/stream/app/http/source/kafka/HttpIngest.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2019 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
+ *
+ *      http://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.cloud.stream.app.http.source.kafka;
+
+import java.util.function.Function;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Import;
+
+
+@SpringBootApplication
+@Import(org.springframework.cloud.stream.app.http.source.HttpSourceConfiguration.class)
+public class HttpIngest {
+
+	@Bean
+	public Function<String, Long> sendAsUserClicks() {
+		return value -> Long.parseLong(value);
+	}
+
+	public static void main(String[] args) {
+		SpringApplication.run(HttpIngest.class, args);
+	}
+}

kafka-samples/http-ingest/src/main/resources/application.yml

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+spring.cloud.stream.kafka.binder.configuration.key:
+  serializer: org.apache.kafka.common.serialization.StringSerializer
+spring.cloud.stream.kafka.binder.configuration.value:
+  serializer: org.apache.kafka.common.serialization.StringSerializer
+spring.cloud.stream.bindings.output.producer:
+  useNativeEncoding: true