Remove deprecated `io/ioutil` from projects

[hiddeco]

All of our projects make use of Go 1.16, and io/ioutil has been deprecated since this version: https://golang.org/doc/go1.16#ioutil

We should remove all traces in our projects and replace them with the suggestions from the deprecation notice.

https://github.com/search?q=ioutil+org%3Afluxcd&type=code

[krishnaindani]

Are there still changes to be made with this issue, could I work on this?

[josephwoodward]

Judging by the merged pull requests above, this issue is no longer relevant and can be closed?

[allenporter]

There are still many to cleanup: https://github.com/search?q=ioutil+org%3Afluxcd&type=code