add support for building via a docker container [remote dev]

docker/mkbuilder.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+SCRIPT_DIR=$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )
+D=$(date +'%Y%m%d.%H%M%S%3N')
+
+set -e
+
+cd "${SCRIPT_DIR}/.."
+# Create the builder image
+docker build \
+    -t flutter-builder-obtainium \
+    -f ./docker/Dockerfile \
+    --build-arg="DEV_UID=$(id -u)" \
+    .