Add support for search API

[alea12]

@yujinakayama Thanks for the repo. It helped me getting started with Apple Music API with ease 🙂
I've added support for the GET https://api.music.apple.com/v1/catalog/{storefront}/search endpoint.

Expected use case is as follows:

const res = await client.search.get('Ed Sheeran', { storefront: 'us' });

[KoreanThinker]

@yujinakayama Can you merge?

[lzilioli]

@KoreanThinker what did you end up doing here?