Enlarge Kafka and MinIO disk size in demo (#124)

## Description

After running the demo for some time kafka's disk run full. We actually had the same thing during the hackathon in Karlsruhe ^^

Author: sbernauer

stacks/kafka-druid-superset-s3/kafka.yaml

@@ -21,7 +21,7 @@ spec:
       resources:
         storage:
           logDirs:
-            capacity: 5Gi
+            capacity: 15Gi
         cpu:
           max: 500m
           min: 250m

stacks/stacks-v1.yaml

@@ -12,7 +12,7 @@ _templates:
         rootPassword: rootroot
         mode: standalone
         persistence:
-          size: 10Gi
+          size: 15Gi
         users:
           - accessKey: druid
             secretKey: druiddruid