initial project setup

In this commit we set up the basic project structure.
- An integ crate that will serve as our driver for integration testing.
  Eventually this will be used to set up and run Bottlerocket instances
  that the updater can be tested against.
- The updater crate. This will become the binary that checks and updates
  Bottlerocket instances.
- A simple Dockerfile and Makefile, since we will be deploying the
  updater to Fargate.

updater has a lib.rs file so that we can re-use some code from updater
in integ, and so that updater can have a useful tests directory.

Makefile

@@ -0,0 +1,32 @@
+BOTTLEROCKET_SDK_VERSION ?= 0.15.0
+BOTTLEROCKET_SDK_SITE    ?= cache.bottlerocket.aws
+LOCAL_ARCH               ?= $(shell uname -m)
+TARGET_ARCH              ?= x86_64
+
+# the docker image that will be used to compile rust code
+BUILDER_IMAGE ?= bottlerocket/sdk-$(TARGET_ARCH):v$(BOTTLEROCKET_SDK_VERSION)-$(LOCAL_ARCH)
+
+# the target triple that will be passed to the cargo build command with as --target
+RUST_TARGET ?= $(TARGET_ARCH)-bottlerocket-linux-musl
+
+.PHONY: image # creates a docker image with the updater binary
+image: fetch-sdk
+	DOCKER_BUILDKIT=1 \
+	docker build \
+		-t bottlerocket-ecs-updater:latest \
+		--build-arg BUILDER_IMAGE=${BUILDER_IMAGE} \
+		--build-arg RUST_TARGET=${RUST_TARGET} \
+		"${PWD}/updater"
+
+.PHONY: fetch-sdk
+fetch-sdk: # fetches and loads the image we use to build the updater docker image
+	set -eou pipefail; \
+	if ! docker image inspect ${BUILDER_IMAGE} >/dev/null 2>&1; then \
+	  if ! curl --fail --show-error https://${BOTTLEROCKET_SDK_SITE}/${BUILDER_IMAGE}.tar.gz \
+		| gunzip | docker load; then \
+	  echo "failed to load '${BUILDSYS_SDK_IMAGE}'" >&2; \
+	  exit 1; \
+	  fi \
+	else \
+	  echo "${BUILDER_IMAGE} is already loaded"; \
+	fi