rpk: sample config to include empty structs

Sample config file had empty properties:
pandaproxy and schema_registry; rpk strips them
out due to the omitempty struct tag.

In the past viper assumed the presence of a
property was enough to include it in the file,
that didn't respect the omitempty tag.

conf/redpanda.yaml

@@ -45,10 +45,10 @@ redpanda:
   developer_mode: true
 
 # Enable Pandaproxy
-pandaproxy:
+pandaproxy: {}
 
 # Enable Schema Registry
-schema_registry:
+schema_registry: {}
 
 rpk:
   # TLS configuration.

src/go/rpk/pkg/config/params_test.go

@@ -78,6 +78,85 @@ rpk:
     kafka_api:
         brokers:
             - 127.0.1.1:9647
+`,
+		},
+		{
+			name: "read/write sample redpanda.yaml",
+			inCfg: `organization: ""
+cluster_id: ""
+license_key: ""
+redpanda:
+  data_directory: "/var/lib/redpanda/data"
+  node_id: 1
+  seed_servers: []
+  rpc_server:
+    address: "0.0.0.0"
+    port: 33145
+  kafka_api:
+  - address: "0.0.0.0"
+    port: 9092
+  admin:
+    address: "0.0.0.0"
+    port: 9644
+  developer_mode: true
+pandaproxy: {}
+schema_registry: {}
+rpk:
+  enable_usage_stats: true
+  tune_network: false
+  tune_disk_scheduler: false
+  tune_disk_nomerges: false
+  tune_disk_irq: false
+  tune_fstrim: false
+  tune_cpu: false
+  tune_aio_events: false
+  tune_clocksource: false
+  tune_swappiness: false
+  enable_memory_locking: false
+  tune_coredump: false
+  coredump_dir: "/var/lib/redpanda/coredump"
+`,
+			exp: `config_file: /etc/redpanda/redpanda.yaml
+redpanda:
+    data_directory: /var/lib/redpanda/data
+    node_id: 1
+    seed_servers: []
+    rpc_server:
+        address: 0.0.0.0
+        port: 33145
+    kafka_api:
+        - address: 0.0.0.0
+          port: 9092
+    admin:
+        - address: 0.0.0.0
+          port: 9644
+    developer_mode: true
+rpk:
+    kafka_api:
+        brokers:
+            - 0.0.0.0:9092
+    admin_api:
+        addresses:
+            - 127.0.0.1:9644
+    enable_usage_stats: true
+    tune_network: false
+    tune_disk_scheduler: false
+    tune_disk_nomerges: false
+    tune_disk_write_cache: false
+    tune_disk_irq: false
+    tune_fstrim: false
+    tune_cpu: false
+    tune_aio_events: false
+    tune_clocksource: false
+    tune_swappiness: false
+    tune_transparent_hugepages: false
+    enable_memory_locking: false
+    tune_coredump: false
+    coredump_dir: /var/lib/redpanda/coredump
+    tune_ballast_file: false
+    overprovisioned: false
+pandaproxy: {}
+schema_registry: {}
 `,
 		},
 	}