[stable/prometheus-pushgateway] Follow the Call for maintainers (#18662)

* Follow the Call for maintainers

As this Chart is bad/not maintained and also buggy I would like to take
ownership for this Chart as my team relies on this Chart.

Signed-off-by: cstaud <christian.staude@staffbase.com>

* Bump version

Signed-off-by: cstaud <christian.staude@staffbase.com>

* Add newline

Signed-off-by: cstaud <christian.staude@staffbase.com>

* Add OWNERS to .helmignore

Signed-off-by: cstaud <christian.staude@staffbase.com>

stable/prometheus-pushgateway/.helmignore

@@ -19,3 +19,6 @@
 .project
 .idea/
 *.tmproj
+
+# OWNERS file for Kubernetes
+OWNERS

stable/prometheus-pushgateway/Chart.yaml

@@ -2,7 +2,7 @@ apiVersion: v1
 appVersion: "1.0.0"
 description: A Helm chart for prometheus pushgateway
 name: prometheus-pushgateway
-version: 1.2.0
+version: 1.2.1
 home: https://github.com/prometheus/pushgateway
 sources:
 - https://github.com/prometheus/pushgateway
@@ -12,3 +12,5 @@ keywords:
 maintainers:
 - email: gianrubio@gmail.com
   name: gianrubio
+- email: christian.staude@staffbase.com
+  name: cstaud

stable/prometheus-pushgateway/OWNERS

@@ -1,4 +1,6 @@
 approvers:
 - gianrubio
+- cstaud
 reviewers:
-- gianrubio
+- gianrubio
+- cstaud