Switch to npm workspaces (#342)

* Switch to npm workspaces
* Install npm globally

Co-authored-by: Christian Georgi <chgeo@users.noreply.github.com>
Co-authored-by: Christian Georgi <christian.georgi@sap.com>

.github/workflows/node.js.yml

@@ -24,5 +24,6 @@ jobs:
       uses: actions/setup-node@v1
       with:
         node-version: ${{ matrix.node-version }}
+    - run: npm i -g npm@8
     - run: npm ci
     - run: npm test