Security scan fixes - gosec

[limak9182]

Description

Handle previously ignored error return values from ctrl.SetControllerReference in the PostgreSQL cluster builder functions, flagged by gosec (G104 / CWE-703).

Key Changes

• pkg/postgresql/cluster/core/cluster.go: buildCNPGCluster and buildCNPGPooler now return error, propagating SetControllerReference failures to callers. Updated call sites at the reconciler level (Reconcile) and createConnectionPooler to handle the new error.
• pkg/postgresql/cluster/core/cluster_unit_test.go: Updated tests for TestBuildCNPGCluster, TestBuildCNPGPooler/rw_pooler, and TestBuildCNPGPooler/ro_pooler to assert no error on the new return signature.

Testing and Verification

• All existing unit tests pass (go test ./pkg/postgresql/cluster/core/ -v)
• gosec no longer reports G104 on cluster.go:567 and cluster.go:726

Related Issues

CPI-1859

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.

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[M4KIF]

Important, nice to see static analysis related fixes.