Change stack version requirements due to the breaking changes (elastic#15268)

The metric name queue.filled.pct.events was changed to queue.filled.pct in v8.15.0.

We've previously fixed the metric name in the package fields. However, the minimal stack version requirements remained unchanged. This would break any customers running on stack versions 8.11.2 – 8.14.3 and upgrading their Elastic Agent integration to 2.5.2.

Author: rdner

packages/elastic_agent/changelog.yml

@@ -1,8 +1,13 @@
 # newer versions go on top
 
+- version: "2.6.0"
+  changes:
+    - description: Update version requirements due to the breaking change in metric names
+      type: enhancement
+      link: "https://github.com/elastic/integrations/pull/15268"
 - version: "2.5.2"
   changes:
-    - description: Update `queue.filled.pct.events` to `queue.filled.pct` metric name 
+    - description: Update `queue.filled.pct.events` to `queue.filled.pct` metric name
       type: enhancement
       link: "https://github.com/elastic/integrations/pull/15244"
 - version: "2.5.1"

packages/elastic_agent/manifest.yml

@@ -1,13 +1,13 @@
 name: elastic_agent
 title: Elastic Agent
-version: 2.5.2
+version: 2.6.0
 description: Collect logs and metrics from Elastic Agents.
 type: integration
 format_version: 3.1.4
 categories: ["elastic_stack"]
 conditions:
   kibana:
-    version: "^8.11.2 || ^9.0.0"
+    version: "^8.15.0 || ^9.0.0"
   elastic:
     subscription: basic
 owner: