[Backport 8.x] Mark data lifecycle APIs as stable (#3109) (#3117)

Author: pquentin

output/schema/schema-serverless.json

@@ -4,7 +4,7 @@
       "url": "https://www.elastic.co/guide/en/elasticsearch/reference/master/data-streams-delete-lifecycle.html",
       "description": "Deletes the data stream lifecycle of the selected data streams."
     },
-    "stability": "experimental",
+    "stability": "stable",
     "visibility": "public",
     "headers": {
       "accept": ["application/json"]

output/schema/schema.json

@@ -4,7 +4,7 @@
       "url": "https://www.elastic.co/guide/en/elasticsearch/reference/current/data-streams-explain-lifecycle.html",
       "description": "Retrieves information about the index's current data stream lifecycle, such as any potential encountered error, time since creation etc."
     },
-    "stability": "experimental",
+    "stability": "stable",
     "visibility": "public",
     "headers": {
       "accept": ["application/json"]

specification/_json_spec/indices.delete_data_lifecycle.json

@@ -4,7 +4,7 @@
       "url": "https://www.elastic.co/guide/en/elasticsearch/reference/master/data-streams-get-lifecycle.html",
       "description": "Returns the data stream lifecycle of the selected data streams."
     },
-    "stability": "experimental",
+    "stability": "stable",
     "visibility": "public",
     "headers": {
       "accept": ["application/json"]

specification/_json_spec/indices.explain_data_lifecycle.json

@@ -4,10 +4,11 @@
       "url": "https://www.elastic.co/guide/en/elasticsearch/reference/master/data-streams-put-lifecycle.html",
       "description": "Updates the data stream lifecycle of the selected data streams."
     },
-    "stability": "experimental",
+    "stability": "stable",
     "visibility": "public",
     "headers": {
-      "accept": ["application/json"]
+      "accept": ["application/json"],
+      "content_type": ["application/json"]
     },
     "url": {
       "paths": [