fix set non-empty applied condition reason for invalid profiles

[ucpr]

What does this PR do?

Fix empty reason field in DatadogAgentProfile status condition that causes Kubernetes API validation errors.

When a profile fails validation, the Applied condition was set with empty Reason and Message fields. Kubernetes requires reason to be at least 1 character, so the status update was rejected.

Motivation

The operator was logging the following error continuously:

{"level":"ERROR","ts":"2026-03-15T15:59:24.713Z","logger":"controllers.DatadogAgent","msg":"unable to update profile status","datadogagentprofile":"system","datadogagentprofile_namespace":"datadog","error":"DatadogAgentProfile.datadoghq.com \"system\" is invalid: status.conditions[1].reason: Invalid value: \"\": conditions[1].reason in body should be at least 1 chars long","stacktrace":"github.com/DataDog/datadog-operator/internal/controller/datadogagent.(*Reconciler).reconcileProfiles\n\t/workspace/internal/controller/datadogagent/profile.go:77\ngithub.com/DataDog/datadog-operator/internal/controller/datadogagent.(*Reconciler).reconcileInstanceV3\n\t/workspace/internal/controller/datadogagent/controller_reconcile_v2.go:96\ngithub.com/DataDog/datadog-operator/internal/controller/datadogagent.(*Reconciler).internalReconcileV2\n\t/workspace/internal/controller/datadogagent/controller_reconcile_v2.go:53\ngithub.com/DataDog/datadog-operator/internal/controller/datadogagent.(*Reconciler).Reconcile\n\t/workspace/internal/controller/datadogagent/controller.go:124\ngithub.com/DataDog/datadog-operator/internal/controller.(*DatadogAgentReconciler).Reconcile\n\t/workspace/internal/controller/datadogagent_controller.go:216\nsigs.k8s.io/controller-runtime/pkg/reconcile.(*objectReconcilerAdapter[...]).Reconcile\n\t/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.20.4/pkg/reconcile/reconcile.go:154\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller[...]).Reconcile\n\t/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.20.4/pkg/internal/controller/controller.go:119\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller[...]).reconcileHandler\n\t/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.20.4/pkg/internal/controller/controller.go:334\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller[...]).processNextWorkItem\n\t/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.20.4/pkg/internal/controller/controller.go:294\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller[...]).Start.func2.2\n\t/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.20.4/pkg/internal/controller/controller.go:255"}

This prevented profile status from being updated when validation failed.

Additional Notes

The fix sets Reason: "Invalid" and Message: "Profile is not valid" for the Applied condition when the profile is invalid, consistent with how other conditions use InvalidConditionReason to indicate the cause.

Minimum Agent Versions

N/A - operator-only change, no agent version requirement.

Describe your test plan

Confirmed that make test passes all tests.

Checklist

• PR has at least one valid label: bug, enhancement, refactoring, documentation, tooling, and/or dependencies
• PR has a milestone or the qa/skip-qa label
• All commits are signed (see: signing commits)

[ucpr]

I don't have permission to add labels, so could you please add them for me?