Expose inspectSwarmNodeCmd through DockerClient - #2673

Summary

• expose the existing InspectSwarmNodeCmd through DockerClient
• delegate the new client method and wire it to the existing command implementation and executor
• add swarm integration coverage that inspects a node by ID

Root cause

The command interface, implementation, and executor already existed, but DockerClient and DockerClientDelegate did not expose a factory method. Consumers therefore could not invoke the command through the public client API.

Impact

Consumers can now call dockerClient.inspectSwarmNodeCmd(nodeId).exec() consistently with the existing list, update, and remove swarm-node commands.

Verification

• mvn -pl docker-java-api,docker-java-core -am test -DskipITs -Dmaven.javadoc.skip=true
• mvn -pl docker-java -am test-compile -DskipITs -Dmaven.javadoc.skip=true
• git diff --check
• Full mvn clean install -DskipITs passed through the API, core, transport TCK, Netty, and Jersey modules; it stopped in the existing OkHttp Docker-dependent TCK because no local Docker daemon was available.

Fixes #2373