Support custom URL of apkIndexArchive

What do you think about support custom apkIndexArchiveURL via environment variable or other ways ?

Lines 53 to 55 in 00f4474

    
           const ( 
        
           	apkIndexArchiveURL = "https://raw.githubusercontent.com/knqyf263/apkIndex-archive/master/alpine/v%s/main/x86_64/history.json" 
        
           )

Case: This feature is needed for run trivy client in internal environment which can't access internet and/or github.com.

	const (
	apkIndexArchiveURL = "https://raw.githubusercontent.com/knqyf263/apkIndex-archive/master/alpine/v%s/main/x86_64/history.json"
	)