feat(metrics): Add span.system tag to span metrics (#3913)

In anticipation of the new MongoDB support that is being added to the
Insights Queries module, this PR will add the `span.system` tag to
metrics. This will allow for querying all database systems in a
particular project, so that users can switch the view of the queries
module based on their choice of DBMS.

CHANGELOG.md

@@ -18,6 +18,7 @@
 - Introduce `trim = "disabled"` type attribute to prevent trimming of spans. ([#3877](https://github.com/getsentry/relay/pull/3877))
 - Make the tcp listen backlog configurable and raise the default to 1024. ([#3899](https://github.com/getsentry/relay/pull/3899))
 - Extract `user.geo.country_code` into span indexed. ([#3911](https://github.com/getsentry/relay/pull/3911))
+- Add `span.system` tag to span metrics ([#3913](https://github.com/getsentry/relay/pull/3913))
 
 ## 24.7.1
 

relay-dynamic-config/src/defaults.rs

@@ -905,6 +905,10 @@ pub fn hardcoded_span_metrics() -> Vec<(GroupKey, Vec<MetricSpec>, Vec<TagMappin
                         Tag::with_key("trace.status")
                             .from_field("span.sentry_tags.trace.status")
                             .when(is_queue_op.clone()),
+                        // database module
+                        Tag::with_key("span.system")
+                            .from_field("span.sentry_tags.system")
+                            .when(is_db.clone()),
                     ],
                 },
                 TagMapping {