feat: Add crossplane_managed_resource_* state metrics

[lkiii]

Description of your changes

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

Metrics exposed:

• 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 is labeled with GVK (GroupVersionKind). Polls every 30 seconds.

Implementation:

• Added pkg/controller/statemetrics.go with SetupStateMetrics() function
• Registers MRStateRecorder for all 22 managed resource types (PostgreSQL, MySQL, MSSQL - both cluster and namespaced)
• Added unit tests in pkg/controller/statemetrics_test.go

Fixes #307

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable to ensure this PR is ready for review.

How has this code been tested

• All unit tests pass (make reviewable)
• Manual end-to-end testing verified metrics are exposed correctly at :8080/metrics
• Created a test Database resource and confirmed crossplane_managed_resource_exists incremented from 0 to 1 after the 30-second poll interval