chore(dynamic-sampling): add hint about conditions in dynamic sampling rules (#14303)

Author: shellmayr

develop-docs/application-architecture/dynamic-sampling/architecture.mdx

@@ -52,6 +52,18 @@ An example of rule encoded in JSON is the following:
 }
 ```
 
+<Alert title="✨ Note">
+Dynamic sampling rules must always include a `condition` field, otherwise the entire dynamic sampling ruleset will be ignored by Relay. If you want a rule to match every event, set the condition as follows:
+```json
+{
+  "condition": {
+    "inner": [],
+    "op": "and"
+  }
+}
+```
+</Alert>
+
 #### Fetching the Sampling Configuration
 
 The sampling configuration is fetched by Relay from Sentry in a pull fashion. This is done by sending a request to the `/api/0/relays/projectconfigs/` endpoint periodically (defined [here](https://github.com/getsentry/sentry/blob/master/src/sentry/api/endpoints/relay/project_configs.py#L34-L34)).