Replace deprecated ioutil pkg with os & io

[abhinavnair]

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.

So replacing all usage of ioutil pkg with io & os.

[YaroslavPodorvanov]

@kamilogorek this PR safe

[cleptric]

@abhinavnair Would you be so kind as to update the Changelog.md and include a note similar to https://github.com/getsentry/sentry-go/blob/master/CHANGELOG.md#v0120 letting folks know that versions before 1.16 won't work anymore?

[kamilogorek]

LGTM. @cleptric we will update support note once #470 is merged, just prior to releasing next version.

[kamilogorek]

It looks like something got stuck in GH actions. @abhinavnair can you push an empty commit to retrigger checks? git commit --allow-empty --allow-empty-message -m ""

[smeubank]

i was just looped in here, and possibly I am being a bit overcautious 😅 . And I'm no expert in Go, we just see some significant number of events coming in for sub 1.16 Go versions. So I am wondering if this breaking change can be based on some version dependency check from the SDK?

[smeubank]

any thoughts on my post above? @kamilogorek maybe we just need to make a decision here on what to do

[vladanpaunovic]

Together with @smeubank , we'll follow up on this, respecting our depreciation policy.