Improve before_send_transactiondocs (#6509)

Co-authored-by: Anton Pirker <[email protected]>

Author: cleptric

src/platform-includes/configuration/before-send-transaction/python.mdx

@@ -1,4 +1,4 @@
-In Python a function can be used to modify the transaction event or return a completely new one. If you return `None`, the event will be discarded.
+In Python, a function can be used to modify the transaction event or return a new instance. If you return `None`, the event will be discarded.
 
 ```python
 import sentry_sdk
@@ -13,3 +13,23 @@ sentry_sdk.init(
     before_send_transaction=strip_sensitive_data,
 )
 ```
+
+Addtionally, you may filter out transaction events based on the request URL, like `/healthcheck`.
+
+```python
+from urllib.parse import urlparse
+
+def filter_transactions(event, hint):
+    url_string = event["request"]["url"]
+    parsed_url = urlparse(url_string)
+
+    if parsed_url.path == "/healthcheck":
+        return None
+
+    return event
+
+sentry_sdk.init(
+    # ...
+    before_send_transaction=filter_transactions,
+)
+```