Setup CI to download from GitHub Packages registry

CI now supports fetching packages from the GitHub Packages registry on
draft PRs. This is meant to support the use of "preview" builds of
controller packages, to more easily test controller changes before they
are released.

.github/workflows/ci.yml

@@ -25,6 +25,18 @@ jobs:
         with:
           path: ${{ steps.yarn-cache-dir.outputs.YARN_CACHE_DIR }}
           key: yarn-cache-${{ runner.os }}-${{ steps.yarn-version.outputs.YARN_VERSION }}-${{ hashFiles('yarn.lock') }}
+      - name: Determine whether the current PR is a draft
+        id: set-is-draft
+        if: github.event_name == 'pull_request' && github.event.pull_request.number
+        run: echo "IS_DRAFT=$(gh pr view --json isDraft --jq '.isDraft' ${PR_NUMBER})" >> "$GITHUB_OUTPUT"
+        env:
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      - name: Setup registry config for using package previews on draft PRs
+        if: github.event_name == 'pull_request' && steps.set-is-draft.outputs.IS_DRAFT == 'true'
+        run: printf '%s\n\n%s' '@metamask:registry=https://npm.pkg.github.com' "//npm.pkg.github.com/:_authToken=${PACKAGE_READ_TOKEN}" > .npmrc
+        env:
+          PACKAGE_READ_TOKEN: ${{ secrets.PACKAGE_READ_TOKEN }}
       - run: yarn setup
       - uses: actions/cache@v3
         id: restore-build