Add language detect API

[mkozakov]

response = await cohere.detectLanguage({ texts: ["hello", "привет"] });

console.log(response.results[0].language_code) // "en"
console.log(response.results[0].language_name) // "English"
console.log(response.results[0].confidence) // 0.9

console.log(response.results[1].language_code) // "ru"
console.log(response.results[1].language_name) // "Russian"
console.log(response.results[1].confidence) // 0.93