ES|QL: Add breaking change note for brackets in index names

Author: luigidellaquila

docs/changelog/130427.yaml

@@ -1,5 +1,25 @@
 pr: 130427
-summary: Disallow brackets in unquoted index pattersn
+summary: Disallow brackets in unquoted index patterns
 area: ES|QL
-type: bug
-issues: []
+type: breaking
+issues:
+  - 130378
+breaking:
+  title: Unquoted index patterns do not allow `(` and `)` characters
+  area: ES|QL
+  details: >-
+    So far, ES|QL accepted unquoted index patterns containing brackets, eg.
+
+    ```
+    FROM index(1) | ENRICH policy(2)
+    ```
+
+    This can potentially conflict with subquery syntax, that uses brackets as a delimiter.
+    From now on, using brackets is only allowed in quoted index patterns, ie. the query above is no longer valid,
+    while the following is valid
+
+    ```
+    FROM "index(1)" | ENRICH "policy(2)"
+    ```
+  impact: "It impacts all the queries that contain brackets in index names or policy names, ie. in FROM, ENRICH and LOOKUP JOIN commands"
+  notable: false