Add network option for image building

This commit adds configuration to the Maven and Gradle plugins to
allow specifying the network mode to be provided to the image
building goal and task.

See gh-27486

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/docs/asciidoc/packaging-oci-image.adoc

@@ -169,6 +169,14 @@ Where `<options>` can contain:
 | `--publishImage`
 | Whether to publish the generated image to a Docker registry.
 | `false`
+
+| `network`
+| `--network`
+| The network the build container will connect to. The value supplied for this option will be passed
+unvalidated as `HostConfig.NetworkMode` to the configuration which creates the build container,
+see https://docs.docker.com/engine/api/v1.41/#operation/ContainerCreate[Docker's engine API].
+Using this option is similar to running `docker build --network ...`.
+|
 |===
 
 NOTE: The plugin detects the target Java compatibility of the project using the JavaPlugin's `targetCompatibility` property.