Get out of `io/ioutil` module because it is deprecated

[alvinlin123]

I was working on #4817, and got bunch of lint error about io/ioutil is deprecated. I tried to fixed some while upgrading to Go 1.19, but there are just too many violations, so I will ignore https://staticcheck.io/docs/checks#SA1019 for now in golangci.yml, and come back to it later on.

https://pkg.go.dev/io/ioutil has info on which package to migrate to.

[yeya24]

As #4851 has been merged, are we ready to close this now?

[alvinlin123]

Argh, yes we should. I forgot to close it. Thanks for the reminder.