ES|QL: Add breaking change note for brackets in index names (elastic#131012) (elastic#131035)

Author: luigidellaquila

docs/changelog/130427.yaml

@@ -1,5 +1,17 @@
 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: >-
+    Previously, ES|QL accepted unquoted index patterns containing brackets, such as `FROM index(1) | ENRICH policy(2)`.
+
+    This query syntax is no longer valid because it could conflict with subquery syntax, where brackets are used as delimiters.
+
+    Brackets are now only allowed in quoted index patterns. For example: `FROM "index(1)" | ENRICH "policy(2)"`.
+  impact: "This affects existing queries containing brackets in index or policy names, i.e. in FROM, ENRICH, and LOOKUP JOIN commands."
+  notable: false