Add changelog generator and scripts to update files

.github_changelog_generator

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+project=vmpooler-dns-google-clouddns
+user=puppetlabs
+exclude_labels=maintenance

update-changelog

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+#!/usr/bin/env bash
+
+docker run -it --rm -e CHANGELOG_GITHUB_TOKEN -v $(pwd):/usr/local/src/your-app \
+  githubchangeloggenerator/github-changelog-generator:1.16.2 \
+  github_changelog_generator --future-release $(grep VERSION lib/vmpooler-dns-google-clouddns/version.rb |rev |cut -d "'" -f2 |rev)

update-gemfile-lock

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+#!/usr/bin/env bash
+
+# The container tag should closely match what is used in `docker/Dockerfile` in vmpooler-deployment
+docker run -it --rm \
+  -v $(pwd):/app \
+  jruby:9.3.6-jdk \
+  /bin/bash -c 'apt-get update -qq && apt-get install -y --no-install-recommends make git && cd /app && gem install bundler && bundle install --jobs 3 && bundle update; echo "LOCK_FILE_UPDATE_EXIT_CODE=$?"'