fix: trim CRLF from password read from stdin

bufio's reader.ReadString includes any CRLF characters and we don't
want these in the resulting token because this leads to errors in the
authentication like this:

```
✗ failed to get Git repository
"https://github.com/kingdon-ci/jenkins-infra": Get
"https://api.github.com/repos/kingdon-ci/jenkins-infra": net/http:
invalid header field value "Bearer gho_NNNNNsecrettokenMMMMM\n" for
key Authorization
```

Signed-off-by: Max Jonas Werner <mail@makk.es>

cmd/flux/main.go

@@ -22,6 +22,7 @@ import (
 	"log"
 	"os"
 	"path/filepath"
+	"strings"
 	"time"
 
 	"github.com/spf13/cobra"
@@ -171,6 +172,9 @@ func homeDir() string {
 	return os.Getenv("USERPROFILE") // windows
 }
 
+// readPasswordFromStdin reads a password from stdin and returns the input
+// with trailing newline and/or carriage return removed. It also makes sure that terminal
+// echoing is turned off if stdin is a terminal.
 func readPasswordFromStdin(prompt string) (string, error) {
 	var out string
 	var err error
@@ -187,5 +191,5 @@ func readPasswordFromStdin(prompt string) (string, error) {
 		return "", fmt.Errorf("could not read from stdin: %w", err)
 	}
 	fmt.Println()
-	return out, nil
+	return strings.TrimRight(out, "\r\n"), nil
 }