feat(shard-distributor): add GetMetadata and GetNamespace methods to executor interface (#7477)

**What changed?**
Added `GetMetadata()` and `GetNamespace()` methods to the Executor
interface, with implementations in executorImpl and updated mocks.

**Why?**
Allow components that interact with executors to access their metadata
(like gRPC address) and namespace without additional lookups. This is
needed for the canary ping handler to identify which executor is
responding.

**How did you test it?**
Verified methods return correct values. Updated mock to include new
methods.

**Potential risks**
None - this only adds interface methods that return existing data.

**Release notes**

**Documentation Changes**
None

Signed-off-by: Jakob Haahr Taankvist <[email protected]>

Author: jakobht

service/sharddistributor/client/executorclient/client.go

@@ -45,6 +45,9 @@ type Executor[SP ShardProcessor] interface {
 
 	GetShardProcess(ctx context.Context, shardID string) (SP, error)
 
+	// Get the namespace this executor is responsible for
+	GetNamespace() string
+
 	// Set metadata for the executor
 	SetMetadata(metadata map[string]string)
 	// Get the current metadata of the executor

service/sharddistributor/client/executorclient/clientimpl.go

@@ -462,6 +462,10 @@ func (e *executorImpl[SP]) emitMetricsConvergence(converged bool) {
 	}
 }
 
+func (e *executorImpl[SP]) GetNamespace() string {
+	return e.namespace
+}
+
 func (e *executorImpl[SP]) SetMetadata(metadata map[string]string) {
 	e.metadata.Set(metadata)
 }