enhance(help): render flags of parent commands

[brandon1024]

It would be great if the default usage/help templates would also render the flags of all parent commands.

Flags:
  -a <address>, --addr=<address>
      The remote address and port of the microinverter (e.g. 192.0.2.1:14889).

  -h
      show command usage information

  --help
      show command help information

  --poll-interval=<duration>
      Configure a deadline for the inverter to respond to poll messages (e.g. 10s). If zero (0s), no deadline is configured and the client will wait indefinitely. A small deadline will cause the client to poll the inverter more frequently.

  --reconnect-interval=<duration> (default 1m0s)
      Interval between connection attempts (e.g. 1m) when the inverter connection is lost, which typically occurs when the inverter enters low power mode during sundown.

  -s <serial>, --serial-number=<serial>
      The serial number of your microinverter (e.g. 31583078).

Flags for "server":
  --web.disable-exporter-metrics
      Exclude metrics about the exporter itself (go_*).

  --web.listen-address=<address> (default :9090)
      The address on which to listen for requests.

  --web.telemetry-path=<path> (default /metrics)
      The path under which to expose metrics.

Flags for "openevt":
  --log.level=<level> (default INFO)
      Application level (e.g. DEBUG, INFO, WARN, ERROR).