feat: add devcontainer support for judgels development

This patch add initial configs for devcontainer, development inside
container using vscode.
https://code.visualstudio.com/docs/devcontainers/containers

To use it, simply open judgels as follow:

$ git clone https://github.com/ia-toki/judgels.git
$ cd judgels
$ code .

Different container runtimes might need additional step. For example,
with colima on macOS, the source code directory need to be mounted on
start such as follow:

$ colima start --cpu 6 --memory 16 --mount $JUDGELS_HOME:$JUDGELS_HOME:w

Where $JUDGELS_HOME is an environment variable to judgels source code
path in host filesystem.

Testing:
- Successfully compile the code with devcontainer on macOS

.devcontainer/Dockerfile

@@ -0,0 +1,14 @@
+FROM ubuntu:20.04
+
+ARG USER_UID=1000
+ARG USER_GID=$USER_UID
+
+RUN apt-get update \
+    && apt-get install -y sudo git \
+    && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends tzdata \
+    && addgroup --gid "${USER_GID}" tokidev \
+    && adduser --uid "${USER_UID}" --gid "${USER_GID}" --disabled-password --gecos '' tokidev \
+    && echo 'tokidev ALL=(ALL) NOPASSWD:ALL' >> /etc/sudoers
+
+EXPOSE 9101
+EXPOSE 3000

.devcontainer/devcontainer.json

@@ -0,0 +1,17 @@
+{
+  "name": "Impala Dev",
+  "dockerFile": "Dockerfile",
+  "runArgs": [
+    "--privileged",
+  ],
+  "remoteUser": "tokidev",
+  "containerUser": "tokidev",
+  "postCreateCommand": "echo 'yes' | bin/bootstrap_system.sh",
+  "customizations": {
+    "vscode": {
+      "extensions": [
+        "vscjava.vscode-java-pack"
+      ]
+    }
+  }
+}

bin/bootstrap_system.sh

@@ -0,0 +1,61 @@
+#!/usr/bin/env bash
+
+# This script is intended to install the minimum requirement to start
+# developing judgels in ubuntu20.04
+
+set -eu -o pipefail
+
+: ${JUDGELS_HOME:=$(cd "$(dirname $0)"/..; pwd)}
+export JUDGELS_HOME
+
+if [[ -t 1 ]] # if on an interactive terminal
+then
+  echo "This script will clobber some system settings. Are you sure you want to"
+  echo -n "continue? "
+  while true
+  do
+    read -p "[yes/no] " ANSWER
+    ANSWER=$(echo "$ANSWER" | tr /a-z/ /A-Z/)
+    if [[ $ANSWER = YES ]]
+    then
+      break
+    elif [[ $ANSWER = NO ]]
+    then
+      echo "OK, Bye!"
+      exit 1
+    fi
+  done
+fi
+
+set -x
+
+# install tools via apt-get
+UBUNTU_JAVA_VERSION="11"
+sudo apt-get --yes install git ssh wget curl unzip vim-common \
+  openjdk-${UBUNTU_JAVA_VERSION}-jdk openjdk-${UBUNTU_JAVA_VERSION}-source \
+  openjdk-${UBUNTU_JAVA_VERSION}-dbg npm mysql-client
+
+# setup mysql server as a separate docker container, such as:
+# docker run --name mysql -e MYSQL_ROOT_PASSWORD=judgels-root \
+#   -e MYSQL_DATABASE=judgels -d mysql:8
+
+# install yarn
+sudo npm install --global yarn
+
+java --version
+npm --version
+yarn --version
+
+# assemble judgels-server-app
+cd $JUDGELS_HOME/judgels-backends/judgels-server-app
+cp var/conf/judgels-server.yml.example var/conf/judgels-server.yml
+../gradlew assemble
+
+# build judgels-client
+cd $JUDGELS_HOME/judgels-client
+cp public/var/conf/judgels-client.js.example public/var/conf/judgels-client.js
+yarn install
+
+# TODO: to start judgels-server-app and judgels-client,
+# follow the remaining instruction at:
+# https://github.com/ia-toki/judgels/wiki/Dev's-Guide:-Running-from-source

bin/create-mysql-user.sql

@@ -0,0 +1,3 @@
+CREATE USER 'judgels'@'%' IDENTIFIED WITH mysql_native_password BY 'judgels';
+GRANT ALL PRIVILEGES ON * . * TO 'judgels'@'%';
+FLUSH PRIVILEGES;

judgels-backends/.gitignore

@@ -8,6 +8,7 @@ generated_tests/
 
 data/
 
+.devcontainer/*
 .idea/
 .ideaDataSources/
 *.iml