[O11y][GCP] Update fields in GCP Load balancing dashboards

[rajvi-patel-22]

Description

GCP Load balancing dashboards are not being populated when integration is configured.
The logs are being stored as gcp.loadbalancing_metrics.*. But dashboards are using gcp.loadbalancing.* field.

Below is the PR in which the pipeline was updated.
[GCP] Add loadbalancing ingest pipeline: #4350

Screenshot