Increment profiler version at release time

### Describe request or inquiry
The `@google-cloud/profiler` is used in our services to produce profiling information and to track issue when something is noticed. The profiler is always initialized with a version. This version needs to be updated and maintained with releases of the applications so that whenever we notice a sudden issue with the latest release, we can compare profiling information against previous version.

Since the first release of the sample app, the profiler version has never been updated. (see [currencyservice](https://github.com/GoogleCloudPlatform/microservices-demo/blob/master/src/currencyservice/server.js#L25), [paymentservice](https://github.com/GoogleCloudPlatform/microservices-demo/blob/master/src/paymentservice/index.js#L22) and [frontend](https://github.com/GoogleCloudPlatform/microservices-demo/blob/master/src/frontend/main.go#L106) as examples) . This version should match sample application release version.

Thus, we must add steps in the release process documentation to instruct the `release-owner` to manually create PRs for updating the `profiler version` on the release branches. We should then later add automation to update these versions automatically during the release process.

Doing this will ensure that we can filter through [profiler data](https://pantheon.corp.google.com/profiler;timespan=10m;end=2021-11-25T17:35:00.000Z/paymentservice;type=HEAP/space?project=onlineboutique-ci) by release version and compare them to see where resource utilization has changed over time. This enables tracking down issues like #538 easier.

### What purpose/environment will this feature serve?
- Troubleshooting and debugging issues with the app in newer releases
- Identifying adverse effects of new code changes and feature inclusions

Start with the profiler version references in src/currencyservice/server.js, src/paymentservice/index.js, and src/frontend/main.go, then locate the release process documentation. Document the release-owner steps for creating PRs that update profiler versions on release branches, ensuring they match the sample application release version.

Written by the indexing model from the issue text.