feat: metadata support in the kubernetes_sync (#1905)

## This PR
- Preserve FeatureFlag metadata when syncing from Kubernetes by
marshalling `spec.flagSpec` directly from unstructured objects.
- Harden informer tombstone handling and watcher readiness for
Kubernetes sync.
- Add unit tests covering metadata preservation and tombstone unwrap.

### Related Issues
Fixes # #754 (CRD definition is not following the latest flagD
specifications) - in the
[open-feature-operator](https://github.com/open-feature/open-feature-operator)
already rased the pr for open-feature-operator CRD support for metaData
- (open-feature/open-feature-operator#808
that alone is not enough, so in Flagd also want to change. This PR
refers to that.

### Notes
- Architecture unchanged; only Kubernetes sync path touched.
- No dependency/version changes.

### Follow-up Tasks
- None.
This change keeps the Kubernetes sync path working with metadata by
treating FeatureFlag resources as unstructured objects and marshaling
spec.flagSpec directly. That avoids converting into typed CRDs (which
can drop unknown fields like metadata) and ensures delete tombstones are
handled safely, so the synced payload now preserves any metadata the CRD
allows.

### How to test
1) From repo root:
- `cd core && GOPATH=/tmp/go GOCACHE=/tmp/go-build go test
./pkg/sync/kubernetes`
2) (Optional) Build and run your existing workflow to confirm metadata
is present end-to-end.

---------

Signed-off-by: Nilushiya.K <Nilushiya.K@cloudsolutions.com.sa>
Signed-off-by: Todd Baert <todd.baert@dynatrace.com>
Signed-off-by: Nilushiya Kaneshalingam <107831659+Nilushiya@users.noreply.github.com>
Co-authored-by: Nilushiya.K <Nilushiya.K@cloudsolutions.com.sa>
Co-authored-by: Todd Baert <todd.baert@dynatrace.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Michael Beemer <beeme1mr@users.noreply.github.com>

Author: 5 people

core/go.mod

@@ -13,7 +13,7 @@ require (
 	github.com/google/uuid v1.6.0
 	github.com/hashicorp/go-memdb v1.3.5
 	github.com/open-feature/flagd-schemas v0.2.13
-	github.com/open-feature/open-feature-operator/apis v0.2.45
+	github.com/open-feature/open-feature-operator/api v0.2.47
 	github.com/prometheus/client_golang v1.23.2
 	github.com/robfig/cron v1.2.0
 	github.com/santhosh-tekuri/jsonschema/v6 v6.0.2
@@ -89,7 +89,6 @@ require (
 	github.com/emicklei/go-restful/v3 v3.12.0 // indirect
 	github.com/envoyproxy/go-control-plane/envoy v1.36.0 // indirect
 	github.com/envoyproxy/protoc-gen-validate v1.3.0 // indirect
-	github.com/evanphx/json-patch/v5 v5.9.0 // indirect
 	github.com/felixge/httpsnoop v1.0.4 // indirect
 	github.com/fxamacker/cbor/v2 v2.7.0 // indirect
 	github.com/go-jose/go-jose/v4 v4.1.4 // indirect
@@ -129,9 +128,6 @@ require (
 	github.com/spf13/pflag v1.0.6 // indirect
 	github.com/spiffe/go-spiffe/v2 v2.6.0 // indirect
 	github.com/x448/float16 v0.8.4 // indirect
-	github.com/xeipuuv/gojsonpointer v0.0.0-20190905194746-02993c407bfb // indirect
-	github.com/xeipuuv/gojsonreference v0.0.0-20180127040603-bd5ef7bd5415 // indirect
-	github.com/xeipuuv/gojsonschema v1.2.0 // indirect
 	go.opencensus.io v0.24.0 // indirect
 	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
 	go.opentelemetry.io/contrib/bridges/prometheus v0.67.0 // indirect
@@ -159,21 +155,19 @@ require (
 	golang.org/x/text v0.35.0 // indirect
 	golang.org/x/time v0.11.0 // indirect
 	golang.org/x/xerrors v0.0.0-20240903120638-7835f813f4da // indirect
-	gomodules.xyz/jsonpatch/v2 v2.4.0 // indirect
 	google.golang.org/api v0.235.0 // indirect
 	google.golang.org/genproto v0.0.0-20250603155806-513f23925822 // indirect
 	google.golang.org/genproto/googleapis/api v0.0.0-20260401024825-9d38bb4040a9 // indirect
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20260401024825-9d38bb4040a9 // indirect
 	gopkg.in/evanphx/json-patch.v4 v4.12.0 // indirect
 	gopkg.in/inf.v0 v0.9.1 // indirect
 	k8s.io/api v0.33.2 // indirect
-	k8s.io/apiextensions-apiserver v0.31.1 // indirect
 	k8s.io/klog/v2 v2.130.1 // indirect
 	k8s.io/kube-openapi v0.0.0-20250318190949-c8a335a9a2ff // indirect
-	k8s.io/utils v0.0.0-20241104100929-3ea5e8cea738 // indirect
-	sigs.k8s.io/controller-runtime v0.19.3 // indirect
+	k8s.io/utils v0.0.0-20241210054802-24370beab758 // indirect
+	sigs.k8s.io/controller-runtime v0.20.1 // indirect
 	sigs.k8s.io/gateway-api v1.2.1 // indirect
-	sigs.k8s.io/json v0.0.0-20241010143419-9aa6b5e7a4b3 // indirect
+	sigs.k8s.io/json v0.0.0-20241014173422-cfa47c3a1cc8 // indirect
 	sigs.k8s.io/randfill v1.0.0 // indirect
 	sigs.k8s.io/structured-merge-diff/v4 v4.6.0 // indirect
 	sigs.k8s.io/yaml v1.4.0 // indirect