[ILM] rolling upgrade tests (#35328)

Adds basic rolling upgrade tests to check that lifecycles are still recognizable between rolling cluster upgrades and managed indices stay managed.

This is a placeholder for discussing types of checks so they are ready once we backported

This is a re-boot of the previous PR against index-lifecycle that needed to be
reverted due to CI bwc issues. #32828

Author: talevy

x-pack/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/mixed_cluster/70_ilm.yml

@@ -0,0 +1,31 @@
+---
+"Test Set Policy On Index":
+  - do:
+      ilm.get_lifecycle:
+        policy: "my_lifecycle"
+  - match: { my_lifecycle.policy.phases.warm.min_age: "1000d" }
+
+  - do:
+      ilm.explain_lifecycle:
+        index: "my_old_index"
+  - is_true: indices.my_old_index.managed
+  - match: { indices.my_old_index.index: "my_old_index" }
+  - match: { indices.my_old_index.policy: "my_lifecycle" }
+
+  - do:
+      indices.create:
+        index: my_mixed_index
+        body:
+          settings:
+            index.lifecycle.name: "my_lifecycle"
+
+  - do:
+      ilm.explain_lifecycle:
+        index: "my_mixed_index"
+  - is_true: indices.my_mixed_index.managed
+  - match: { indices.my_mixed_index.index: "my_mixed_index" }
+  - match: { indices.my_mixed_index.policy: "my_lifecycle" }
+
+  - do:
+      indices.delete:
+        index: my_mixed_index

x-pack/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/old_cluster/70_ilm.yml

@@ -0,0 +1,49 @@
+---
+"Test Basic Policy Creation":
+  - do:
+      catch: missing
+      ilm.get_lifecycle:
+        policy: "my_lifecycle"
+
+  - do:
+      catch: missing
+      ilm.delete_lifecycle:
+        policy: "my_lifecycle"
+
+  - do:
+      ilm.put_lifecycle:
+        policy: "my_lifecycle"
+        body: |
+           {
+             "policy": {
+               "phases": {
+                 "warm": {
+                   "min_age": "1000d",
+                   "actions": {
+                     "forcemerge": {
+                       "max_num_segments": 10000
+                     }
+                   }
+                 }
+               }
+             }
+           }
+
+  - do:
+      ilm.get_lifecycle:
+        policy: "my_lifecycle"
+  - match: { my_lifecycle.policy.phases.warm.min_age: "1000d" }
+
+  - do:
+      indices.create:
+        index: my_old_index
+        body:
+          settings:
+            index.lifecycle.name: "my_lifecycle"
+
+  - do:
+      ilm.explain_lifecycle:
+        index: "my_old_index"
+  - is_true: indices.my_old_index.managed
+  - match: { indices.my_old_index.index: "my_old_index" }
+  - match: { indices.my_old_index.policy: "my_lifecycle" }

x-pack/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/upgraded_cluster/70_ilm.yml

@@ -0,0 +1,21 @@
+---
+"Test Lifecycle Still There And Indices Are Still Managed":
+  - do:
+      ilm.get_lifecycle:
+        policy: "my_lifecycle"
+  - match: { my_lifecycle.policy.phases.warm.min_age: "1000d" }
+
+  - do:
+      ilm.explain_lifecycle:
+        index: "my_old_index"
+  - is_true: indices.my_old_index.managed
+  - match: { indices.my_old_index.index: "my_old_index" }
+  - match: { indices.my_old_index.policy: "my_lifecycle" }
+
+  - do:
+      indices.delete:
+        index: my_old_index
+
+  - do:
+      ilm.delete_lifecycle:
+        policy: "my_lifecycle"