[#22729][#22730] yugabyted: APIServer and UI implementation for xcluster in yugabyted

Summary:
API Server and UI implementation for XCluster in Yugabyted

Three new endpoints:
1. `/api/xcluster_metrics`
2. `/api/xcluster_namespace_details/:replication_id`
3. `/api/xcluster_safe_time_metrics`

The third endpoint is not currently in use and will support historical data fetching once the `consumer_time_lag` field is exposed to Prometheus.
Jira: DB-11634, DB-11635

Test Plan: Manual testing

Reviewers: sgarg-yb, nikhil, djiang

Reviewed By: nikhil, djiang

Subscribers: krishna.tripathi, yugabyted-dev

Differential Revision: https://phorge.dev.yugabyte.com/D41347

Author: krishna-yb

yugabyted-ui/apiserver/cmd/server/.docs/api/openapi.yaml

@@ -52,6 +52,7 @@ models/model_metric_data.go
 models/model_metric_response.go
 models/model_migrate_schema_task_info.go
 models/model_migration_assessment_report.go
+models/model_namespaces_info.go
 models/model_node_data.go
 models/model_node_data_cloud_info.go
 models/model_node_data_metrics.go
@@ -77,6 +78,7 @@ models/model_sql_objects_details.go
 models/model_table_info.go
 models/model_table_info_table_replication_info.go
 models/model_table_replication_info.go
+models/model_table_replication_lag_details_outbound.go
 models/model_tablet_info.go
 models/model_target_cluster_recommendation_details.go
 models/model_target_cluster_spec.go
@@ -91,4 +93,10 @@ models/model_voyager_migration_details_source_db.go
 models/model_voyager_migration_details_target_cluster.go
 models/model_voyager_migration_details_voyager.go
 models/model_voyager_migrations_info.go
+models/model_x_cluster_inbound_group.go
+models/model_x_cluster_namespace_metrics.go
+models/model_x_cluster_outbound_group.go
+models/model_x_cluster_placement_location.go
+models/model_x_cluster_replication_groups.go
+models/model_x_cluster_table_info_inbound.go
 models/model_yb_api_enum.go