Add service ping settings options to orbit

What does this MR do and why?

Exposes Service Ping settings on the internal Orbit endpoint (GET /api/v4/internal/orbit/instance) so Orbit can follow the instance's Service Ping configuration, not only the product usage data setting.

This adds three new fields under settings:

• service_ping_enabled - whether Service Ping is enabled and consented
• service_ping_generation_enabled - whether Service Ping generation is enabled
• service_ping_optional_metrics_enabled - whether optional metrics are enabled

These use the same helpers Rails' own Service Ping uses (ServicePing::ServicePingSettings.enabled_and_consented?, usage_ping_generation_enabled?, usage_ping_features_enabled?), ensuring Orbit can't drift from Rails' behavior.

This is Part A of the related issue. Part B (adding "Orbit is turned on" metric to Rails Service Ping) will be handled separately.

How it works with existing test coverage:

Setting	gitlab.yml locks it off	Online customer_service_enabled? license	Offline cloud license	Tests
service_ping_enabled	false	forced to true, even when gitlab.yml is off (still false if consent is pending)	no effect	CE, EE
service_ping_generation_enabled	follows the generation checkbox	no effect*	no effect*	model
service_ping_optional_metrics_enabled	false	no effect*, stays false unless Service Ping is on in gitlab.yml and the admin settings	no effect*	gitlab.yml off, DB and EE options

References

Related to https://gitlab.com/gitlab-org/analytics-section/analytics-instrumentation/internal/-/work_items/993

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