docker: introduce devcontainers

.devcontainer/devcontainer.json

@@ -0,0 +1,10 @@
+{
+    "name": "seastar-devcontainer",
+    "build": {
+        "dockerfile": "Dockerfile",
+        "context": "../"
+    },
+    "workspaceMount": "source=${localWorkspaceFolder},target=/workspaces/seastar,type=bind,consistency=default",
+    "workspaceFolder": "/workspaces/seastar",
+    "shutdownAction": "stopContainer"
+}

.dockerignore

@@ -1,2 +1,3 @@
+.devcontainer
 .git
 build

doc/building-devcontainer.md

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+## Building seastar using devcontainers
+
+A development container (or devcontainer for short) allows you to use a container as a full-featured development environment. It can be used to run an application, to separate tools, libraries, or runtimes needed for working with a codebase, and to aid in continuous integration and testing.
+
+You can build a project with [devcontainers](https://containers.dev/) in an easy and convenient way.
+Your IDE (e.g. Clion) or code editor (e.g. VS Code) can run and [attach](https://containers.dev/supporting) to devcontainer.
+
+Also you can use [devcontainers/cli](https://github.com/devcontainers/cli) to set up environment and build the project manually via bash:
+
+```bash
+devcontainer up --workspace-folder .
+
+devcontainer exec --workspace-folder . \
+  ./configure.py --mode=release
+
+devcontainer exec --workspace-folder . \
+  ninja -C build/release
+```
+
+It's just a more powerful and convenient version of [building-docker](./building-docker.md)