Add flag allow-error-in-defer

[maratori]

Add flag allow-error-in-defer. If enabled, linter doesn't complain about named error, if it is assigned inside defer.

func GoodFunc() (err error) {
	defer func() {
		err = nil
	}()
	return
}

Open question: should this flag be enabled by default? Now it's not.

Fixes #5

[firefart]

awesome thanks for this PR!

[maratori]

I'll prepare PR to add config into golangci-lint tomorrow.

[maratori]

I created golangci/golangci-lint#2915 (draft) and will update it after new release of nonamedreturns.

[maratori]

They use dependabot and update config in it's PR (I will do it).

[firefart]

@maratori thanks I've released v1.0.2 just now: https://github.com/firefart/nonamedreturns/releases/tag/v1.0.2