GH-530, GH-630 Improvements to AWS Custom Runtime

This commit provides initial set of improvements to executing functions in AWS Custom Runtime
- Consistent invocation model for functional as well as @Bean configuration models via new CustomRuntimeEventLoop as well as AWSLambdaUtils
- Clean up classpath to decrease the size of the JAR/ZIP file
- Configuration simplification which no longer requires enabling of function exporter

It also allows user to define functions that rely on AWS types such as APIGatewayProxyRequestEvent

The existing invocation model remains in tact for the time being. Both invocation models are mutually exclusing in theit setup to avoid potential conflict.

Resolves #538
Resolves #630

spring-cloud-function-samples/function-sample-aws-custom-bean/src/assembly/zip.xml

@@ -0,0 +1,35 @@
+<assembly xmlns="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.2"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.2 https://maven.apache.org/xsd/assembly-1.1.2.xsd">
+	<id>zip</id>
+	<formats>
+		<format>zip</format>
+	</formats>
+	<baseDirectory></baseDirectory>
+	<fileSets>
+		<fileSet>
+			<directory>target/classes</directory>
+			<outputDirectory>/</outputDirectory>
+			<useDefaultExcludes>true</useDefaultExcludes>
+			<excludes>
+				<exclude>bootstrap</exclude>
+			</excludes>
+		</fileSet>
+		<fileSet>
+			<directory>target/classes</directory>
+			<outputDirectory>/</outputDirectory>
+			<useDefaultExcludes>true</useDefaultExcludes>
+			<fileMode>0775</fileMode>
+			<includes>
+				<include>bootstrap</include>
+			</includes>
+		</fileSet>
+	</fileSets>
+	<dependencySets>
+		<dependencySet>
+			<outputDirectory>/lib</outputDirectory>
+			<unpack>false</unpack>
+			<scope>runtime</scope>
+		</dependencySet>
+	</dependencySets>
+</assembly>