Add group all support for Prometheus Alertmanager (SchemaStore#5085)

* Add group all support for Prometheus Alertmanager

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---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: POPSuL

src/negative_test/prometheus-alertmanager/mix-3dots-and-labels.yml

@@ -0,0 +1,8 @@
+# yaml-language-server: $schema=../../schemas/json/prometheus-alertmanager.json
+
+route:
+  group_by: [..., cluster]
+  routes:
+    - matchers:
+        - service=~"foo1|foo2|baz"
+      group_by: [..., cluster]

src/schemas/json/prometheus-alertmanager.json

@@ -241,11 +241,26 @@
           "type": "string"
         },
         "group_by": {
-          "type": "array",
-          "items": {
-            "$ref": "#/definitions/labelname"
-          },
-          "description": "The labels by which incoming alerts are grouped together"
+          "anyOf": [
+            {
+              "type": "array",
+              "minItems": 1,
+              "additionalItems": false,
+              "description": "Group by all labels",
+              "items": [
+                {
+                  "enum": ["..."]
+                }
+              ]
+            },
+            {
+              "type": "array",
+              "items": {
+                "$ref": "#/definitions/labelname"
+              },
+              "description": "The labels by which incoming alerts are grouped together"
+            }
+          ]
         },
         "continue": {
           "type": "boolean",

src/test/prometheus-alertmanager/group-all.yaml

@@ -0,0 +1,9 @@
+# yaml-language-server: $schema=../../schemas/json/prometheus-alertmanager.json
+
+route:
+  group_by: [...]
+  routes:
+    - matchers:
+        - service=~"foo1|foo2|baz"
+      group_by:
+        - ...