Increase fetch timeout / make it configurable

[ignatenkobrain]

terragrunt/util/fetch.go

Lines 20 to 22 in 945145b

	resp, err := (&http.Client{
	Timeout: time.Minute * 1,
	}).Do(req)

Downloading some providers (e.g. AWS one) on slow network does not have to finish within 1 minute so I would suggest to increase default timeout to something like 5 minutes.

And/or make this optional configurable would be useful for those who want to be stricter.

Thanks in advance.