Move dockerfiles into their own directory (#14549)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

.buildkite/run-tpu-v1-test.sh

@@ -3,7 +3,7 @@
 set -e
 
 # Build the docker image.
-docker build -f Dockerfile.tpu -t vllm-tpu .
+docker build -f docker/Dockerfile.tpu -t vllm-tpu .
 
 # Set up cleanup.
 remove_docker_container() { docker rm -f tpu-test || true; }