use sync/errgroup

[komuw]

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Now,

What(What have you changed/added/removed?)

• Use golang.org/x/sync/errgroup for managing goroutine lifecycles.
  TODO: fix todo's

Why(Why did you change/add/remove it?)

• it looks to be better at it

[komuw]

The ci failure is

go: verifying github.com/docker/[email protected]: checksum mismatch
	downloaded: h1:yo5xsA6ZV6CbKtryIlqxspayS5FLU3cHS0SpbFQORbQ=
	go.sum:     h1:v8cqbUr9o2JRb+4rIDWPmncYtTLuXZZprbD7ggflCU8=
Exited with code 1

I think it will be resolved when w move to Go1.13.
go1.12 -> go1.13 has some mod hash mismatches(i read that somewhere, i think)