Improve the concurrent integration test workflow

### TL;DR

The current workflow uses Cloud Run tagging URLs to call individual revisions for each pull request. The original decision to use Cloud Run revisions was for performance reasons.

There are 2 options:

1) Refactor GCLB for Cloud Run to use [URL masks](https://cloud.google.com/load-balancing/docs/https/setting-up-https-serverless#using-url-mask) for targeting tagged revisions

2) Use Terraform to create the entire set of resources per Pull Request and destroy them after.

### Expected behavior

_No response_

### Observed behavior

_No response_

### Environment Details

Integration

### Additional information

_No response_