Update hooks for azd 0.8.0

azd version 0.8.0 packs the application before creating azure resources (when running azd up)
Then `azd deploy` use the output from that packing to publish the app to Azure.
The `predeploy` hook is not valid anymore on this scenario to include the frontend to the backend. Instead, we need to switch to use `prepackage` for the backend service, so the frontend is attached before creating the package.

azure.yaml

@@ -8,6 +8,18 @@ services:
     project: ./app/backend
     language: py
     host: appservice
+    hooks:
+      prepackage:
+        windows:
+          shell: pwsh
+          run:  cd ../frontend;npm install;npm run build
+          interactive: true
+          continueOnError: false
+        posix:
+          shell: sh
+          run:  cd ../frontend;npm install;npm run build
+          interactive: true
+          continueOnError: false
 hooks:
     postprovision:
       windows:
@@ -20,14 +32,3 @@ hooks:
         run: ./scripts/prepdocs.sh
         interactive: true
         continueOnError: false
-    predeploy:
-      windows:
-        shell: pwsh
-        run:  cd ./app/frontend;npm install;npm run build
-        interactive: true
-        continueOnError: false
-      posix:
-        shell: sh
-        run:  cd ./app/frontend;npm install;npm run build
-        interactive: true
-        continueOnError: false