Fix problems signaled by new linter version v1.45.2

PR (linter: upgrade linter version #405) triggered lint job which failed
with many errors generated by various linters. Configurations were added to
golangcilint.yaml and several refactorings were made in order to improve the
results of the linter.

maintidx linter disabled

Signed-off-by: Alex Stan <alexandrustan96@yahoo.ro>

errors/errors.go

@@ -4,6 +4,7 @@ import "errors"
 
 var (
 	ErrBadConfig               = errors.New("config: invalid config")
+	ErrCliBadConfig            = errors.New("cli: bad config")
 	ErrRepoNotFound            = errors.New("repository: not found")
 	ErrRepoIsNotDir            = errors.New("repository: not a directory")
 	ErrRepoBadVersion          = errors.New("repository: unsupported layout version")