CI: Cache/restore the npm network/package cache

This saves/restores the caches of just the packages as source code.
Not the installed and/or compiled versions, which are in node_modules.
(We have already been caching those for some time now.)

Co-Authored-By: deedeeg <[email protected]>

Author: aminya

script/vsts/platforms/templates/bootstrap.yml

@@ -28,4 +28,5 @@ steps:
       GITHUB_TOKEN: $(GITHUB_TOKEN)
       CI: true
       CI_PROVIDER: VSTS
+      npm_config_cache: $(Agent.BuildDirectory)/npm_package_cache_dir
     condition: or(ne(variables['MainNodeModulesRestored'], 'true'), ne(variables['ScriptNodeModulesRestored'], 'true'), ne(variables['ApmNodeModulesRestored'], 'true'))

script/vsts/platforms/templates/cache.yml

@@ -37,3 +37,13 @@ steps:
          npm | "$(Agent.OS)" | "$(BUILD_ARCH)"
       path: 'apm/node_modules'
       cacheHitVar: ApmNodeModulesRestored
+
+  - task: Cache@2
+    displayName: Cache npm package cache
+    inputs:
+      key: 'npm_package_cache | "$(Agent.OS)" | "$(BUILD_ARCH)" | script/package-lock.json, apm/package-lock.json, package-lock.json, script/vsts/platforms/${{ parameters.OS }}.yml'
+      restoreKeys: |
+         npm_package_cache | "$(Agent.OS)" | "$(BUILD_ARCH)" | script/package-lock.json, apm/package-lock.json, package-lock.json
+         npm_package_cache | "$(Agent.OS)" | "$(BUILD_ARCH)"
+         npm_package_cache
+      path: $(Agent.BuildDirectory)/npm_package_cache_dir