refactor: move away from ioutil (deprecated)

What does this MR do?

Move away from io/ioutil.

io/ioutil was deprecated in go 1.16, see https://golang.org/doc/go1.16

TODO

• I added the Changelog trailer (e.g. Changelog: feature) to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines