Add PostgreSQL observability telemetry exposure via ServiceMonitors

[DmytroPI-dev]

Description

Adds PostgreSQL observability telemetry exposure for PostgresCluster with operator-managed metrics Services and Prometheus ServiceMonitors for PostgreSQL and PgBouncer.

Key Changes

api/v4/postgresclusterclass_types.go
Added class-level observability configuration for PostgreSQL and PgBouncer metrics.

api/v4/postgrescluster_types.go
Added cluster-level disable-only observability overrides.

pkg/postgresql/cluster/core/cluster.go
Wired PostgreSQL and PgBouncer metrics Service and ServiceMonitor reconciliation into the PostgresCluster flow.
Made ServiceMonitor presence required by failing reconciliation when the CRD is unavailable.

pkg/postgresql/cluster/core/monitoring.go
Added feature resolution helpers.
Added builders and reconcilers for PostgreSQL/PgBouncer metrics Services.
Added builders and reconcilers for PostgreSQL/PgBouncer ServiceMonitors.

internal/controller/postgrescluster_controller.go
Added RBAC for monitoring.coreos.com/servicemonitors.

cmd/main.go
Registered Prometheus Operator monitoring/v1 types in the manager scheme.

internal/controller/suite_test.go
Registered Prometheus Operator monitoring/v1 types in the test scheme.

pkg/postgresql/cluster/core/monitoring_unit_test.go
Added unit tests for observability flag resolution and monitoring resource builders.

Testing and Verification

Added unit tests in pkg/postgresql/cluster/core/monitoring_unit_test.go for:

• class/cluster observability enablement logic
• PostgreSQL and PgBouncer metrics Service builders
• PostgreSQL and PgBouncer ServiceMonitor builders

Related Issues

CPI-1853 - related JIRA ticket.

PR Checklist

• Code changes adhere to the project's coding standards.
• Relevant unit and integration tests are included.
• Documentation has been updated accordingly.
• All tests pass locally.
• The PR description follows the project's guidelines.