GoogleCloudMonitoring: Add support for numerical comparison operators

[gelicia]

Discussed in https://github.com/grafana/grafana/discussions/66697

^{Originally posted by plutino April 17, 2023} This is a follow up on https://github.com/grafana/grafana/discussions/41822 since it is closed and locked. Please referring to that discussion for details.

The screenshot @andresmgot provided uses a string type label, and regex match works. For numerical type labels as the original request is about, regex match does not work and GCP API still returns the same error:

Field filter had an invalid value of "metric.type="appengine.googleapis.com/http/server/response_count" resource.label.module_id="default" metric.label.response_code=starts_with("4")": Function restrictions are only allowed for string type.

Environment: Grafana version: 9.3.4