Missing system subcommand completion for fish shell

[jhdxr]

Description

Currently completion for docker system and all its subcommand are missing in fish shell.

I'm willing to provide one PR to update the docker.fish file. However I notice manually maintaince for completion script is not recommended as mentioned in #2998 and I don't have much experience or interest in Golang. So before I do anything, I'd like to hear from maintainers about this issue if Cobra Completion is the only option.

[vvoland]

Manual completion scripts are still used and we're not ready to switch to the generated ones yet.
So improvements/fixes in the completions scripts are definitely welcomed.

[jawys]

Hello there!

I'd like to add that these are missing too:

build
builder
buildx
config
container
dev
extension
image
images
info
init
manifest
network
node
plugin
pull
push
sbom
scan
scout
search
service
stack
swarm
system
trust

On the other hand, there are deprecated subcommands being completed:

❯ for cmd in (complete --do-complete 'docker ')
      docker help $cmd >/dev/null
  end
unknown help topic: ecs
unknown help topic: prune
unknown help topic: serve

❯ docker --version
Docker version 24.0.2, build cb74dfc

Because of missing completions for commands like service and node and manifest which are important to me, I started writing my own completions.

BUT I am happy to help fix the completions in the source I one could advise me how to do that!