fix(o11y): add RAR remapper rule for aggregator.filtered_tags (#1823)

## Summary

Adds a RAR remapper rule mapping `adp.tag_filterlist_tags_filtered_total{component_id:dsd_tag_filterlist}` to `aggregator.filtered_tags`, the Core Agent equivalent that tracks how many tags were removed from metric samples by the tag filter.

## Test plan

- [ ] `cargo test -p agent-data-plane` — remapping output and help text tests pass

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: jesse.szwedko <jesse.szwedko@datadoghq.com>

Author: jszwedko

bin/agent-data-plane/src/state/metrics/mod.rs

@@ -823,6 +823,13 @@ mod tests {
                 Context::from_static_parts("adp.tag_filterlist_updates_total", &["component_id:dsd_tag_filterlist"]),
                 11.0,
             )),
+            Event::Metric(Metric::counter(
+                Context::from_static_parts(
+                    "adp.tag_filterlist_tags_filtered_total",
+                    &["component_id:dsd_tag_filterlist"],
+                ),
+                23.0,
+            )),
         ];
 
         for metric in metrics {
@@ -839,6 +846,7 @@ mod tests {
         assert!(output.contains("aggregator__dogstatsd_filtered_metrics 7"));
         assert!(output.contains("tag_filterlist__size 9"));
         assert!(output.contains("tag_filterlist__updates 11"));
+        assert!(output.contains("aggregator__filtered_tags 23"));
         assert!(!output.contains("datadog__agent__filterlist__size"));
         assert!(!output.contains("datadog__agent__filterlist__updates"));
         assert!(!output.contains("datadog__agent__dogstatsd__listener_filtered_points"));
@@ -895,5 +903,9 @@ mod tests {
             get_help_text("tag_filterlist.updates"),
             Some("Incremented when a reconfiguration of the tag filterlist happened")
         );
+        assert_eq!(
+            find("aggregator.filtered_tags"),
+            Some("How many tags were filtered from a metric sample")
+        );
     }
 }

bin/agent-data-plane/src/state/metrics/rules/dogstatsd.rs

@@ -33,6 +33,12 @@ pub fn get_dogstatsd_remappings() -> Vec<RemapperRule> {
             &["component_id:dsd_tag_filterlist"],
             "tag_filterlist.updates",
         ),
+        RemapperRule::by_name_and_tags(
+            "adp.tag_filterlist_tags_filtered_total",
+            &["component_id:dsd_tag_filterlist"],
+            "aggregator.filtered_tags",
+        )
+        .with_help_text("How many tags were filtered from a metric sample"),
         RemapperRule::by_name_and_tags(
             "adp.object_pool_acquired",
             &["pool_name:dsd_packet_bufs"],