Add onpush int-* github action

For coin integration branches, it is necessary to trigger this push to
help testers down the road (Live-common CLI tests).
Any push/merge on int-COIN will push a new @ledgerhq/ledger-core@COIN so
that live-common-only users hopefully don't need a full GCC toolchain to
test the current version in CLI.

It does not not run the yarn version on the Action.
yarn version is actually a hidden git commit so it will trigger an
infinite loop (actually it fails because there are no credentials)

Author: Gerry Agbobada

.github/workflows/coin-integration.yml

@@ -0,0 +1,42 @@
+name: coin-integration-alpha
+on:
+  push:
+    branches:
+      - 'int-*'
+jobs:
+  prebuild-for-platform:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-16.04, macos-latest, windows-2016]
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions/setup-node@master
+        with:
+          node-version: 12.x
+          registry-url: https://registry.npmjs.org
+          always-auth: true
+      - uses: actions/setup-python@v1
+        with:
+          python-version: '2.7.x'
+      - name: install
+        run: yarn --frozen-lockfile --ignore-scripts
+      - name: fetch libcore
+        run: yarn preinstall
+      - name: config gcc
+        if: runner.os == 'Linux'
+        run: sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-7 700 --slave /usr/bin/g++ g++ /usr/bin/g++-7
+      - name: prebuild for electron 8.1
+        run: npx node-pre-gyp configure build package --runtime=electron --target=8.1.0 --build-from-source --dist-url=https://electronjs.org/headers
+      - name: prebuild for electron 8.2
+        run: npx node-pre-gyp configure build package --runtime=electron --target=8.2.0 --build-from-source --dist-url=https://electronjs.org/headers
+      - name: prebuild for node 12
+        run: npx node-pre-gyp configure build package --target=12.16.0
+      - name: Get version and publish @coin on NPM
+        if: matrix.os == 'ubuntu-16.04'
+        env:
+          NODE_AUTH_TOKEN: ${{ secrets.NPM_GAGBO_PUBLISH_TOKEN }}
+        run: |
+            export COIN=$(echo ${GITHUB_REF#refs/heads/int-})
+            echo "I hope you remembered to run 'yarn version --prerelease --preid \"$COIN\"'"
+            yarn publish --tag "$COIN"