feat(flutter): document how to add data to spans/transactions (#12367)

* add span data info to dart

* update flutter page

* Apply suggestions from code review

Co-authored-by: Karl Heinz Struggl <[email protected]>

* Apply suggestions from code review

Co-authored-by: Alex Krawiec <[email protected]>

* Update dart.mdx

* Update dart.mdx

---------

Co-authored-by: Karl Heinz Struggl <[email protected]>
Co-authored-by: Alex Krawiec <[email protected]>

Author: 3 people

docs/platforms/dart/tracing/instrumentation/custom-instrumentation.mdx

@@ -17,3 +17,5 @@ To capture transactions and spans customized to your organization's needs, you m
 <PlatformContent includePath="performance/retrieve-transaction" />
 
 <PlatformContent includePath="performance/connect-errors-spans" />
+
+<PlatformContent includePath="performance/improving-data" />

docs/platforms/flutter/tracing/instrumentation/custom-instrumentation.mdx

@@ -17,3 +17,5 @@ To capture transactions and spans customized to your organization's needs, you m
 <PlatformContent includePath="performance/retrieve-transaction" />
 
 <PlatformContent includePath="performance/connect-errors-spans" />
+
+<PlatformContent includePath="performance/improving-data" />

platform-includes/performance/improving-data/dart.mdx

@@ -0,0 +1,29 @@
+## Adding Data Attributes to Transactions and Spans
+
+You can add data attributes to your transactions and spans. This data is visible in the trace explorer in Sentry. Data attributes can be of type `String`, `int`, `double` or `bool`, as well as (non-mixed) arrays of these types:
+
+### For Transactions
+
+```dart
+final transaction = Sentry.startTransaction('my-transaction', 'http.server');
+transaction.setData('data_attribute_1', 'value1');
+transaction.setData('data_attribute_2', 42);
+transaction.setData('data_attribute_3', true);
+
+transaction.setData('data_attribute_4', ['value1', 'value2']);
+transaction.setData('data_attribute_5', [42, 43]);
+transaction.setData('data_attribute_6', [true, false]);
+```
+
+### For Spans
+
+```dart
+final span = parent.startChild('http.client');
+span.setData('data_attribute_1', 'value1');
+span.setData('data_attribute_2', 42);
+span.setData('data_attribute_3', true);
+
+span.setData('data_attribute_4', ['value1', 'value2']);
+span.setData('data_attribute_5', [42, 43]);
+span.setData('data_attribute_6', [true, false]);
+```