[stable/stackdriver-exporter] deprecating chart (#24399)

Signed-off-by: Matt Farina <matt@mattfarina.com>

stable/stackdriver-exporter/Chart.yaml

@@ -1,7 +1,7 @@
 apiVersion: v1
-description: Stackdriver exporter for Prometheus
+description: DEPRECATED - Stackdriver exporter for Prometheus
 name: stackdriver-exporter
-version: 1.3.1
+version: 1.3.2
 appVersion: 0.6.0
 home: https://www.stackdriver.com/
 sources:
@@ -10,6 +10,4 @@ keywords:
   - metrics
   - stackdriver
   - monitoring
-maintainers:
-  - name: apenney
-    email: apenney@gmail.com
+deprecated: true

stable/stackdriver-exporter/README.md

@@ -18,6 +18,10 @@ access scopes, then you must have
 
 Learn more: https://github.com/frodenas/stackdriver_exporter
 
+## DEPRECATION NOTICE
+
+This chart is deprecated and no longer supported.
+
 ## TL;DR;
 
 ```bash