fix(opentelemetry lib): decode missing scope, schema_url, and resource fields

changelog.d/24905_otlp_decode_missing_fields.fix.md

@@ -0,0 +1,15 @@
+When using Vector's native event format (i.e. `use_otlp_decoding` is
+`false`, the default), the OpenTelemetry source now decodes previously
+dropped OTLP protobuf fields across all signal types, fixing round-trip
+data loss when events pass through Vector between OTLP endpoints.
+
+- **Logs:** `ScopeLogs.schema_url`, `ResourceLogs.schema_url`, and
+  `Resource.dropped_attributes_count` are now preserved.
+- **Traces:** the full `InstrumentationScope` (name, version,
+  attributes, `dropped_attributes_count`), both `schema_url` fields,
+  and `Resource.dropped_attributes_count` are now decoded.
+- **Metrics:** `scope.dropped_attributes_count`, both `schema_url`
+  fields, and `resource.dropped_attributes_count` are now included as
+  metric tags.
+
+authors: szibis