Discrepancy on environment variable naming in Cloud Monitoring backends

[lvaylet]

The project_id variable is referred to as STACKDRIVER_HOST_PROJECT_ID in samples/config.yaml, samples/config_export.yaml and samples.env.sample while samples/README.md mentions a WORKSPACE_PROJECT_ID variable with the same purpose:

samples/config.yaml:

backends:
  cloud_monitoring:
    project_id: ${STACKDRIVER_HOST_PROJECT_ID}
  cloud_monitoring_mql:
    project_id: ${STACKDRIVER_HOST_PROJECT_ID}
  cloud_service_monitoring:
    project_id: ${STACKDRIVER_HOST_PROJECT_ID}

samples/README.md:

### `cloud_monitoring`

| Environment variable | Description |
| --- | --- |
| `WORKSPACE_PROJECT_ID` | Cloud Monitoring host project ID |
[...]

### `cloud_monitoring_mql`

| Environment variable | Description |
| --- | --- |
| `WORKSPACE_PROJECT_ID` | Cloud Monitoring host project ID |
[...]

### `cloud_service_monitoring`

| Environment variable | Description |
| --- | --- |
| `WORKSPACE_PROJECT_ID` | Cloud Monitoring host project ID |
[...]

Users might get confused, even if the explanation is as simple as Google Cloud renaming Stackdriver to Cloud Operations.