Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

internal/cli/ask_credentials.go

@@ -0,0 +1,36 @@
+// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package cli // import "miniflux.app/v2/internal/cli"
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+
+	"golang.org/x/term"
+)
+
+func askCredentials() (string, string) {
+	fd := int(os.Stdin.Fd())
+
+	if !term.IsTerminal(fd) {
+		fmt.Fprintf(os.Stderr, "This is not a terminal, exiting.\n")
+		os.Exit(1)
+	}
+
+	fmt.Print("Enter Username: ")
+
+	reader := bufio.NewReader(os.Stdin)
+	username, _ := reader.ReadString('\n')
+
+	fmt.Print("Enter Password: ")
+
+	state, _ := term.GetState(fd)
+	defer term.Restore(fd, state)
+	bytePassword, _ := term.ReadPassword(fd)
+
+	fmt.Printf("\n")
+	return strings.TrimSpace(username), strings.TrimSpace(string(bytePassword))
+}