Use a GitHub Action to generate the changelog (#9434) [skip ci]

* Use a GitHub Action to generate the changelog

* Update main.workflow [skip ci]

.github/actions/trigger-github-release/Dockerfile

@@ -0,0 +1,18 @@
+FROM node:10
+
+LABEL "name" = "trigger-github-release"
+LABEL "version" = "0.0.1"
+
+LABEL "com.github.actions.name" = "Trigger GitHub release"
+LABEL "com.github.actions.description" = "Trigger a new GitHub release and generate the changelog using lerna-changelog."
+LABEL "com.github.actions.icon" = "tag"
+LABEL "com.github.actions.color" = "yellow"
+
+ADD entrypoint.sh /action/entrypoint.sh
+ADD package.json /action/package.json
+ADD package-lock.json /action/package-lock.json
+ADD release.js /action/release.js
+
+RUN chmod +x /action/entrypoint.sh
+
+ENTRYPOINT ["/action/entrypoint.sh"]

.github/actions/trigger-github-release/entrypoint.sh

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+#!/bin/sh
+
+set -e
+
+echo "INFO: Installing action dependencies..."
+(cd /action; npm ci)
+
+echo "INFO: Checking out current tag..."
+git -c advice.detachedHead=false checkout $GITHUB_REF
+
+echo "INFO: Getting tag info..."
+current_tag=$(git describe --abbrev=0 --tags)
+last_tag=$(git describe --abbrev=0 --tags HEAD^)
+echo "INFO: New version is $current_tag; last version is $last_tag."
+
+echo "INFO: Generating the changelog..."
+
+# lerna-changelog expects the token to be provided as GITHUB_AUTH,
+# but GitHub actions don't allow to predefine custom env vars prefixed with
+# GITHUB_. We need to define it here.
+changelog=$(
+  GITHUB_AUTH="$GITHUB_TOKEN" \
+  node /action/node_modules/.bin/lerna-changelog --tag-from $last_tag --tag-to $current_tag
+)
+
+echo "INFO: Publishing the new GitHub release..."
+echo "$changelog" | node /action/release $current_tag
+
+echo "INFO: Done! Don't forget to thank new contributors :)"