Add a buildbot dir and a script for local testing

.buildbot/node/Dockerfile

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+FROM node:18-bullseye
+
+RUN apt-get update
+RUN apt-get install -yq --no-install-suggests --no-install-recommends xauth xvfb
+
+WORKDIR /app
+ADD src ./src
+COPY package*.json binding.gyp ./
+
+RUN npm install
+# RUN npm audit fix
+
+COPY . .

.buildbot/node/build.sh

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+#!/bin/sh
+
+mkdir -p ../out
+cp package*.json ../out
+npm pack
+mv *.tgz ../out/

.buildbot/node/test.sh

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+#!/bin/sh
+
+npm test

docker-test.sh

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+#!/bin/sh
+docker build --tag bitmessage-js -f .buildbot/node/Dockerfile .
+docker run -it --rm bitmessage-js:latest .buildbot/node/test.sh