The io/ioutil package has been deprecated as of Go 1.16 [1]. This commit
replaces the existing io/ioutil functions with their new definitions in
io and os packages.
[1]: https://golang.org/doc/go1.16#ioutil
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>
The implementation was very heavily docker-local specific and thus didn't make a ton of sense to keep in the cron plugin.
This also re-introduces changes from #5908 to parallelize the crontab generation (which is also specific to the docker-local scheduler) that were lost during a rebase.
The impetus for this change was implementing a `cron:run` command. The logic for actually running the command isn't scheduler specific - merely invoking `dokku run` with the appropriate arguments - but all the logic around how the commands were retrieved were, so the change was made pre-emptively.
