[#414] authmate: Add register-user command

New command allows register user in frostfsid and
set allowed rules in policy contract

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

cmd/s3-authmate/modules/errors.go

@@ -16,6 +16,10 @@ type (
 	frostFSIDInitError struct {
 		err error
 	}
+
+	policyInitError struct {
+		err error
+	}
 )
 
 func wrapPreparationError(e error) error {
@@ -50,6 +54,14 @@ func (e frostFSIDInitError) Error() string {
 	return e.err.Error()
 }
 
+func wrapPolicyInitError(e error) error {
+	return policyInitError{e}
+}
+
+func (e policyInitError) Error() string {
+	return e.err.Error()
+}
+
 // ExitCode picks corresponding error code depending on the type of error provided.
 // Returns 1 if error type is unknown.
 func ExitCode(e error) int {
@@ -62,6 +74,8 @@ func ExitCode(e error) int {
 		return 4
 	case frostFSIDInitError:
 		return 4
+	case policyInitError:
+		return 5
 	}
 	return 1
 }