feat: Add update_pnpm_lock to frontend examples

[RyanDraves]

The aspect_rules_js feature to automatically update the pnpm-lock.yaml file is greatly beneficial for developer experience. This change adds it to the example so folks copying the examples have it out-of-the-box.

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[RyanDraves]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

Signed and re-ran the check.