Fix metrics feature

Metrics feature was relying on old references. Refactored with inspiration from the `get_stats` method in `meilisearch/src/routes/lib.rs`. `enable_metrics_routes` added to options in `segment_analytics`.

Resolves: #3469
See also: #2763

meilisearch/src/analytics/segment_analytics.rs

@@ -249,6 +249,7 @@ impl From<Opt> for Infos {
         // to add analytics when we add a field in the Opt.
         // Thus we must not insert `..` at the end.
         let Opt {
+            enable_metrics_route: _,
             db_path,
             http_addr,
             master_key: _,