feat: Add a chart icon for Artifact Hub (#625)

Author: lfrancke

template/deploy/helm/[[operator]]/Chart.yaml.j2

@@ -6,6 +6,10 @@ appVersion: "<version_placeholder>"
 description: "{[ operator.chart_description }]"
 
 home: https://github.com/stackabletech/{[ operator.name }]
+# One known use of this is the Artifact Hub (AH) listing which shows the logo.
+# AH downloads the logo and re-hosts it.
+# We opted to not use the project logos (e.g. the Apache Spark logo) here due to trademark concerns.
+icon: https://raw.githubusercontent.com/stackabletech/{[ operator.name }]/main/.readme/static/borrowed/Icon_Stackable.svg
 sources:
   - https://github.com/stackabletech/{[ operator.name }]