conf: Update kafka_api to array

[alenkacz]

This should fix #672 and also #524

Even though RPK tries to override this default with array and correct type, viper fails on this because of incompatible types https://github.com/spf13/viper/blob/8c894384998e656900b125e674b8c20dbf87cc06/viper.go#L1828

this is where the deb pkg references it https://github.com/vectorizedio/vtools/blob/79cdd85b11c55e66379a9829e28fe059391a14b6/vtools/artifacts/packaging/debian/debian/redpanda.install#L1

Let's try to think if we break older versions by this?

Checklist

• Reference related issue
• Update PendingReleaseNotes.md, if relevant

When referencing a related issue, remember to migrate duplicate stories from the
external tracker. This is not relevant for most users.

[BenPope]

/gcbrun

[emaxerrno]

what's absolutely wild about this is on my computer if i specify the smae thing for the other addresses, it fails.

❯ cat /etc/redpanda/redpanda.yaml
config_file: /etc/redpanda/redpanda.yaml
node_uuid: SHBk8DEH14SSKv6QySbYYezqPDASDKqCgGAUHs1VekDhJYsDB
redpanda:
  admin:
    address: 0.0.0.0
    port: 9644
  dashboard_dir: /usr/share/redpanda/dashboard                                                                                                                                                                                                                                                                                                                                                                  
  data_directory: /var/lib/redpanda/data
  developer_mode: true
  kafka_api:
    - address: 0.0.0.0
      port: 9092
  node_id: 0
  rpc_server:
    address: 0.0.0.0
    port: 33145
  seed_servers: []
rpk:
  coredump_dir: /var/lib/redpanda/coredump
  enable_memory_locking: false
  enable_usage_stats: false
  overprovisioned: true
  tune_aio_events: false
  tune_clocksource: false
  tune_coredump: false
  tune_cpu: false
  tune_disk_irq: false
  tune_disk_nomerges: false
  tune_disk_scheduler: false
  tune_disk_write_cache: false
  tune_fstrim: false
  tune_network: false
  tune_swappiness: false
  tune_transparent_hugepa

so is only the kafka_api that needs this which is an inconsistency.