[Service] Implement Cloud Monitoring / Metrics (gRPC + REST)

[hectorvent]

Summary

Implement Cloud Monitoring (Metrics) — custom metric ingestion + read. Complements Cloud Logging for observability assertions in tests.

Protocol / transport

gRPC google.monitoring.v3.MetricService + REST.

Authoritative reference

• Proto: local/google/googleapis/google/monitoring/v3/metric_service.proto (+ google/api/metric.proto, monitored_resource.proto in common protos)
• SDK: local/google/google-cloud-java/java-monitoring

Scope (MVP)

• CreateMetricDescriptor, GetMetricDescriptor, ListMetricDescriptors, DeleteMetricDescriptor
• CreateTimeSeries, ListTimeSeries
• ListMonitoredResourceDescriptors
• Store time series keyed by project + metric type + label set

Parity notes

• TimeSeries points = interval + typed value; validate metricKind / valueType.
• ListTimeSeries filter + (basic) aggregation/alignment subset.

Test plan

java-monitoring: create a custom metric descriptor, write a TimeSeries, ListTimeSeries back, assert points + labels.

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Implementation guidance: Follow the google-parity workflow — read the authoritative proto/SDK under local/google/* before implementing, mirror the wire shape exactly, and validate with GCP SDK-based compatibility tests (compatibility-tests/sdk-test-java). See AGENTS.md → "Adding a New GCP Service". Keep storage namespaced by project ID via StorageFactory.

Upstream references (mirrored locally under local/google/*):

• googleapis (proto definitions): https://github.com/googleapis/googleapis
• google-cloud-java (Java SDK source): https://github.com/googleapis/google-cloud-java

[mansiverma897993]

@hectorvent I have raised an another PR Check at once and lemme know if any changes required!!