Parameterize Retry logic to Config

[klauern]

I've been experimenting with different retry logic configurations for different use cases. It would be nice to be able to specify the different retry options in a configuration file, environment variable, or flag (or all 3).

sigil/pkg/aws/aws.go

Lines 93 to 97 in c4ad289

	numMaxRetries = 5
	minRetryDelay = 10 * time.Millisecond
	minThrottleDelay = 500 * time.Millisecond
	maxRetryDelay = 1 * time.Second
	maxThrottleDelay = 4 * time.Second

I currently have a retry policy that is much higher than the default, but I am not sure whether that should be a universal setting, so I would prefer not to force it on everyone using this tool: