Fix add watcher invalid payload issue

[djx339]

Currently, when creating a Jira "Add Watcher" request, the username in playload has been converted from a string type to a []byte type. This change causes the JSON-encoded result is not the username, leading to request failure. Here’s an example. https://go.dev/play/p/pBiwq2t2bNl

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
)

func main() {
	accountID := "someuser"

	buf1 := new(bytes.Buffer)
	if err := json.NewEncoder(buf1).Encode(accountID); err != nil {
		panic(err)
	}
	fmt.Println(buf1)

	buf2 := new(bytes.Buffer)
	if err := json.NewEncoder(buf2).Encode([]byte(accountID)); err != nil {
		panic(err)
	}
	fmt.Println(buf2)
}

output

"someuser"

"c29tZXVzZXI="