Unified Storage: Adds pruner to kv backend (#110549)

* WIP adding pruner to kv store impl

* pruner only keeps 20 most recent versions

* ignore grafana-kv-data folder

* extracts some stuff to pruner.go file. Adds tests. Adds kvBackendOptions.

* update logging, comments, exports kvbackendoptions fields

* update nooppruner ref

* fixes field casing in test

* fix test

* linter fixes

* remove comment

* make KvStorageBackend private

* Adds pruner key validation and tests. Fixes broken tests.

* update error message when validating pruner key

pkg/storage/unified/resource/pruner.go

@@ -0,0 +1,30 @@
+package resource
+
+import "context"
+
+// Pruner Small abstraction to allow for different Pruner implementations.
+// This can be removed once the debouncer is deployed.
+type Pruner interface {
+	Add(key PruningKey) error
+	Start(ctx context.Context)
+}
+
+// PruningKey is a comparable key for pruning history.
+type PruningKey struct {
+	Namespace string
+	Group     string
+	Resource  string
+	Name      string
+}
+
+func (k PruningKey) Validate() bool {
+	return k.Namespace != "" && k.Group != "" && k.Resource != "" && k.Name != ""
+}
+
+type NoopPruner struct{}
+
+func (p *NoopPruner) Add(key PruningKey) error {
+	return nil
+}
+
+func (p *NoopPruner) Start(ctx context.Context) {}