CI: do canary merge and nightly publishing ...

... on the GitHub Actions. This will remove the reliance on the backend
server merging script and more transparent to the other contributors

.github/workflows/publish.yml

@@ -0,0 +1,99 @@
+name: citra-publish
+
+on:
+  schedule:
+    - cron: '7 0 * * *'
+  workflow_dispatch:
+    inputs:
+      nightly:
+        description: 'Whether trigger a nightly build (true/false/auto)'
+        required: false
+        default: 'true'
+      canary:
+        description: 'Whether trigger a canary build (true/false/auto)'
+        required: false
+        default: 'true'
+
+jobs:
+  nightly:
+    runs-on: ubuntu-latest
+    if: ${{ github.event.inputs.nightly != 'false' }}
+    steps:
+      - uses: actions/github-script@v5
+        id: check-changes
+        name: 'Check for new changes'
+        with:
+          result-encoding: string
+          script: |
+            if (context.payload.inputs && context.payload.inputs.nightly === 'true') return true;
+            const delta = new Date() - new Date(context.payload.repository.pushed_at);
+            if (delta <= 86400000) {
+              return true;
+            }
+            console.log('No new changes detected.');
+            return false;
+      # this checkout is required to make sure the GitHub Actions scripts are available
+      - uses: actions/checkout@v2
+        if: ${{ steps.check-changes.outputs.result == 'true' }}
+        name: Pre-checkout
+        with:
+          submodules: false
+      - run: npm install execa@5
+        if: ${{ steps.check-changes.outputs.result == 'true' }}
+      - uses: actions/checkout@v2
+        name: Checkout
+        if: ${{ steps.check-changes.outputs.result == 'true' }}
+        with:
+          path: 'citra-merge'
+          fetch-depth: 0
+          submodules: true
+          token: ${{ secrets.ALT_GITHUB_TOKEN }}
+      - uses: actions/github-script@v5
+        name: 'Update and tag new commits'
+        if: ${{ steps.check-changes.outputs.result == 'true' }}
+        env:
+          ALT_GITHUB_TOKEN: ${{ secrets.ALT_GITHUB_TOKEN }}
+        with:
+          script: |
+            const execa = require("execa");
+            const tagAndPush = require('./.github/workflows/ci-merge.js').tagAndPush;
+            process.chdir('${{ github.workspace }}/citra-merge');
+            tagAndPush(github, context.repo.owner, `${context.repo.repo}-nightly`, execa);
+  canary:
+    runs-on: ubuntu-latest
+    if: ${{ github.event.inputs.canary != 'false' }}
+    steps:
+      # this checkout is required to make sure the GitHub Actions scripts are available
+      - uses: actions/checkout@v2
+        name: Pre-checkout
+        with:
+          submodules: false
+      - uses: actions/github-script@v5
+        id: check-changes
+        name: 'Check for new changes'
+        with:
+          script: |
+            if (context.payload.inputs && context.payload.inputs.canary === 'true') return true;
+            const checkCanaryChanges = require('./.github/workflows/ci-merge.js').checkCanaryChanges;
+            return checkCanaryChanges(github, context);
+      - run: npm install execa@5
+        if: ${{ steps.check-changes.outputs.result == 'true' }}
+      - uses: actions/checkout@v2
+        name: Checkout
+        if: ${{ steps.check-changes.outputs.result == 'true' }}
+        with:
+          path: 'citra-merge'
+          fetch-depth: 0
+          submodules: true
+          token: ${{ secrets.ALT_GITHUB_TOKEN }}
+      - uses: actions/github-script@v5
+        name: 'Check and merge canary changes'
+        if: ${{ steps.check-changes.outputs.result == 'true' }}
+        env:
+          ALT_GITHUB_TOKEN: ${{ secrets.ALT_GITHUB_TOKEN }}
+        with:
+          script: |
+            const execa = require("execa");
+            const mergebot = require('./.github/workflows/ci-merge.js').mergebot;
+            process.chdir('${{ github.workspace }}/citra-merge');
+            mergebot(github, context, execa);