Update error docs to include before_send option (#21275)

#18261 Added support for the `before_send` option when initializing the Sentry SDK in airflow. This patch updates the documentation to reflect this change.
(cherry picked from commit b38391e)

docs/apache-airflow/logging-monitoring/errors.rst

@@ -42,8 +42,14 @@ Add your ``SENTRY_DSN`` to your configuration file e.g. ``airflow.cfg`` in ``[se
 .. note::
     If this value is not provided, the SDK will try to read it from the ``SENTRY_DSN`` environment variable.
 
-You can supply `additional configuration options <https://docs.sentry.io/platforms/python/configuration/options>`__ based on the Python platform via ``[sentry]`` section.
-Unsupported options: ``integrations``, ``in_app_include``, ``in_app_exclude``, ``ignore_errors``, ``before_breadcrumb``, ``before_send``, ``transport``.
+The ``before_send`` option can be used to modify or drop events before they are sent to Sentry. To set this option, provide a dotted path to a before_send function that the sentry SDK should be configured to use.
+
+.. code-block:: ini
+
+    [sentry]
+    before_send = path.to.my.sentry.before_send
+
+You can supply `additional configuration options <https://docs.sentry.io/platforms/python/configuration/options>`__ based on the Python platform via ``[sentry]`` section. Unsupported options: ``integrations``, ``in_app_include``, ``in_app_exclude``, ``ignore_errors``, ``before_breadcrumb``, ``transport``.
 
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