Add Spring Boot Example

[hamiltont]

Thought it would be nice to share this since it took some figuring and it's super useful. Spring boot has a spring-boot:build-image command that can be modified to have this buildpack participate. This is a request to add an example of this usage to the repo's readme. I've documented what I know here:

Multiple buildpack support was added in Spring Boot 2.5.0 (this SB version also requires you update your spring cloud if using that too). By doing the following in pom.xml, you can get this working with maven and SB.

<build>
	<plugin>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-maven-plugin</artifactId>
			<configuration>
				<image>
					<name>yourrepo.com/${artifactId}:${version}</name>
					<buildpacks>
						<buildpack>urn:cnb:builder:paketo-buildpacks/java</buildpack>
						<buildpack>docker://ghcr.io/datadog/datadog-trace-paketo-buildpack/datadog-trace-paketo-buildpack:1.0.0</buildpack>
					</buildpacks>
					<bindings>
						<binding>${project.basedir}/binding:/platform/bindings/DatadogTrace</binding>
					</bindings>
				</image>
			</configuration>
		</plugin>
	</plugins>
</build>

You also need to create a binding directory with the file type (no filename extension) and the contents DatadogTrace. You can optionally create properties or YAML file to list out options like dd.service, or (IIUC) you can use env variables at runtime