Use latest docker garbage collector

[sau226]

This patch configures discourse_docker to use the latest docker_gc version as the version we use was last updated 3 years ago and (in my opinion) a bit slow compared with this version.

[SamSaffron]

@xfalcox should we just pull out docker gc and use the docker built in thing?

[sau226]

Sorry had to sync my local branch. Reopening

[sau226]

That was another forced push (it closes automatically always for some reason). I just toggled allow edits from maintainers (in case you need to update my fork) and will reopen this PR soon

[sau226]

@xfalcox Hiya,

Could you please review this some time to see if docker-gc is still needed?

Regards,

sau226

P.S: Sorry if this request or any of the previous ones are of any inconvenience.

[SamSaffron]

@sau226 I would far prefer a PR that swaps out docker gc and instead has ./launcher cleanup simply invoke docker system prune

[sau226]

@SamSaffron Thanks for the heads up. I've created PR 420 to implement the changes. Please feel free to review that when you're ready.