feat(cli): order flags by categories

[sh0rez]

We have many flags of the form <category>.<name>. This change orders them
groups flags by category.

All flags with no categories and all categories with a single flag only won't be
grouped and will be printed at the top:

Usage of /tmp/go-build531611363/b001/exe/promtail:
   -config.file string:
      yaml file to load
   -log.level value:
      Only log messages with the given severity or above. Valid levels: [debug, info, warn, error] (default info)
   -target.sync-period duration:
      Period to resync directories being watched and files being tailed. (default 10s)
   -version:
      Print this builds version information (default false)

 Client:
   -client.batch-size-bytes int:
      Maximum batch size to accrue before sending.  (default 102400)
   -client.batch-wait duration:
      Maximum wait period before sending batch. (default 1s)
   -client.external-labels value:
      list of external labels to add to each log (e.g: --client.external-labels=lb1=v1,lb2=v2)
   -client.max-backoff duration:
      Maximum backoff time between retries. (default 5s)
   -client.max-retries int:
      Maximum number of retires when sending batches. (default 5)
   -client.min-backoff duration:
      Initial backoff time between retries. (default 100ms)
   -client.timeout duration:
      Maximum time to wait for server to respond to a request (default 10s)
   -client.url value:
      URL of log server

 Positions:
   -positions.file string:
      Location to read/write positions from. (default /var/log/positions.yaml)
   -positions.sync-period duration:
      Period with this to sync the position file. (default 10s)

 Server:
   -server.graceful-shutdown-timeout duration:
      Timeout for graceful shutdowns (default 30s)
   -server.grpc-listen-host string:
      gRPC server listen host.
   -server.grpc-listen-port int:
      gRPC server listen port. (default 9095)
   -server.grpc-max-concurrent-streams uint:
      Limit on the number of concurrent streams for gRPC calls (0 = unlimited) (default 100)
   -server.grpc-max-recv-msg-size-bytes int:
      Limit on the size of a gRPC message this server can receive (bytes). (default 4194304)
   -server.grpc-max-send-msg-size-bytes int:
      Limit on the size of a gRPC message this server can send (bytes). (default 4194304)
   -server.http-idle-timeout duration:
      Idle timeout for HTTP server (default 2m0s)
   -server.http-listen-host string:
      HTTP server listen host.
   -server.http-listen-port int:
      HTTP server listen port. (default 80)
   -server.http-read-timeout duration:
      Read timeout for HTTP server (default 30s)
   -server.http-write-timeout duration:
      Write timeout for HTTP server (default 30s)
   -server.path-prefix string:
      Base path to serve all API routes from (e.g. /v1/)
   -server.register-instrumentation:
      Register the intrumentation handlers (/metrics etc). (default true)

exit status 2

Don't know if it's cool, wanted to try it

[cyriltovena]

Cool for me !