Created new workflow to generate preview envs

.github/workflows/deploy-preview.yml

@@ -0,0 +1,38 @@
+name: Deploy preview
+
+on:
+  pull_request: null
+  push:
+    branches:
+      - main
+
+jobs:
+  deploy:
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+      - name: Use node.js 14.15
+        uses: actions/setup-node@v1
+        with:
+          node-version: 14.15
+      - name: Build
+        run: |
+          npm ci && \
+          npm install json && \
+          node_modules/.bin/json -I -f package.json -e "this.homepage=\"/shlink-web-client/${{ steps.generate_slug.outputs.slug }}\"" && \
+          npm run build
+      - name: Generate slug
+        id: generate_slug
+        run: echo "##[set-output name=slug;]$(echo ${GITHUB_REF#refs/heads/} | sed -r 's/[~\^]+//g' | sed -r 's/[^a-zA-Z0-9]+/-/g' | sed -r 's/^-+\|-+$//g' | tr A-Z a-z)"
+      - name: Deploy
+        uses: JamesIves/github-pages-deploy-action@4.1.1
+        with:
+          branch: preview-env
+          folder: build
+          target-folder: ${{ steps.generate_slug.outputs.slug }}
+      - name: Publish env
+        uses: marocchino/sticky-pull-request-comment@v2
+        with:
+          header: Preview environment
+          message: "**Preview environment**: https://shlinkio.github.io/shlink-web-client/${{ steps.generate_slug.outputs.slug }}"