chore(): update opensource chart version to alpha15, ruler to alpha13 (#175)

## What type of PR is this?

* [ ] Feature
* [ ] BUG
* [ ] Alerts
* [x] Improvement
* [ ] Documentation
* [ ] Test and CI

## What this PR does / why we need it:

update opensource chart version to alpha15, ruler to alpha13

Author: EZ4BRUCE

charts/mo-ob-opensource/Chart.yaml

@@ -2,7 +2,7 @@ apiVersion: v2
 name: mo-ob-opensource
 description: mo-ob-opensource's Helm chart for Kubernetes
 type: application
-version: 1.0.0-alpha.14
+version: 1.0.0-alpha.15
 appVersion: 0.9.0
 dependencies:
 - condition: kube-prometheus-stack.enabled

charts/mo-ruler-stack/Chart.yaml

@@ -2,7 +2,7 @@ apiVersion: v2
 name: mo-ruler-stack
 description: mo-ruler's Helm chart for Kubernetes
 type: application
-version: 1.0.0-alpha.12
+version: 1.0.0-alpha.13
 appVersion: 0.9.0
 dependencies:
 - condition: alertmanager.enabled