add beforeSendTransaction to options list

Author: lobsterkatie

src/platforms/common/configuration/options.mdx

@@ -563,6 +563,18 @@ This function is called with an SDK-specific message or error event object, and
 
 </ConfigKey>
 
+<ConfigKey name="before-send-transaction" supported={["javascript", "node"]}>
+
+This function is called with an SDK-specific transaction event object, and can return a modified transaction event object, or `null` to skip reporting the event. This can be used, for instance, for manual PII stripping before sending.
+
+<PlatformSection supported={["javascript", "node"]}>
+
+_(New in version 7.18.0)_
+
+</PlatformSection>
+
+</ConfigKey>
+
 <ConfigKey name="on-crash" supported={["native"]}>
 
 This function is called with a backend-specific event object, and can return a modified event object or nothing to skip reporting the event. In contrast to `before_send`, it is only called when a crash occured. You can find detailed information concerning its usage in [Filtering](/platforms/native/configuration/filtering/#using-on_crash).