Replace uses of the io/ioutil package

[roberthbailey]

Is your feature request related to a problem? Please describe.
From a code review comment on #2743:
SA1019: "io/ioutil" has been deprecated since Go 1.16: As of Go 1.16, the same functionality is now provided by package io or package os, and those implementations should be preferred in new code. See the specific function documentation for details

Describe the solution you'd like
Remove uses of the io/ioutil package and remove the linter exception.

Describe alternatives you've considered
Leave the deprecated imports and the linter exception in place. The package should remain for the foreseeable future, so it may be ok....