Update helm chart stable repository URL

The stable repository for helm charts was moved to a new URL. The
old one will be unavailable soon.

Change-Id: I34300992764bab012e8dd602d75f19817dcdd7ba

subcommands/install.py

diff --git a/subcommands/install.py b/subcommands/install.py
index 871f797..b4a91d6 100644
--- a/subcommands/install.py
+++ b/subcommands/install.py
@@ -35,7 +35,7 @@
 ]
 
 HELM_REPOS = {
-    "stable": "https://kubernetes-charts.storage.googleapis.com",
+    "stable": "https://charts.helm.sh/stable",
     "loki": "https://grafana.github.io/loki/charts",
 }