feat: Add crossplane_managed_resource_* state metrics

[lkiii]

Summary

Add Prometheus state metrics for all managed resource types, following the Crossplane observability guide.

Motivation

Currently, provider-sql does not expose state metrics for managed resources. These metrics are valuable for:

• Monitoring the health and status of managed resources at scale
• Alerting on resources that are not ready or synced
• Dashboarding resource counts by type and state

Proposed Solution

Implement the following metrics using crossplane-runtime/v2/pkg/statemetrics:

• crossplane_managed_resource_exists - Count of existing managed resources
• crossplane_managed_resource_ready - Count of ready managed resources
• crossplane_managed_resource_synced - Count of synced managed resources

Each metric will be labeled with the GVK (GroupVersionKind) of the resource type.

Implementation Notes

• Register MRStateRecorder for all 22 managed resource types (PostgreSQL, MySQL, MSSQL - both cluster and namespaced)
• Poll interval: 30 seconds
• Add unit tests for the configuration

Related

• Crossplane observability guide: https://github.com/crossplane/crossplane/blob/master/contributing/guide-observability.md