chore: speed up builds by breaking out dev-container again

.devcontainer/BUILD.bazel

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+load("//:hack/publish.bzl", "publish")
+load("@io_bazel_rules_docker//docker/util:run.bzl", "container_run_and_commit_layer")
+load("@io_bazel_rules_docker//container:container.bzl", "container_image")
+
+container_run_and_commit_layer(
+    name = "bazel-layer",
+    commands = [
+        "go get -u github.com/bazelbuild/bazelisk",
+        "ln /go/bin/bazelisk /usr/bin/bazel",
+        "go get -u github.com/bazelbuild/buildtools/...",
+    ],
+    image = "@devcontainergo//image",
+)
+
+container_run_and_commit_layer(
+    name = "node-layer",
+    commands = [
+        "su vscode -c 'source /usr/local/share/nvm/nvm.sh && nvm install lts/* 2>&1'",
+    ],
+    image = "@devcontainergo//image",
+)
+
+container_image(
+    name = "dev-container",
+    base = "@devcontainergo//image",
+    layers = [
+        ":bazel-layer",
+        ":node-layer",
+    ],
+)
+
+publish(
+    name = "publish-dev-container",
+    image = ":dev-container",
+    service = "dev-container",
+)
+
+publish(
+    name = "publish-dev-container-dockerhub",
+    image = ":dev-container",
+    prefix = "roleypoly/",
+    registry = "index.docker.io",
+    service = "dev-container",
+)

.devcontainer/README.md

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+# Dev Container
+
+This package houses the dev-container image.
+
+It includes:
+
+-   go (1.15.2)
+-   bazel (latest via bazelisk)
+-   node (latest lts via nvm)
+
+As well as any other tooling within VSCode Dev Containers.
+
+## Building
+
+To build and use locally,
+
+```sh
+bazel run //srv/dev-container && docker run -it --rm bazel/src/dev-container:dev-container
+```
+
+To just use, this is published to two registries. There is no effective difference, except that GitHub's registry requires login, and Docker Hub does not.
+
+-   `docker pull roleypoly/dev-container:main`
+-   `docker pull docker.pkg.github.com/roleypoly/roleypoly/dev-container:main`