feat: Add support for Artist Sort Name

[veroxzik]

Since Artist Sort Name is supported by OpenSubsonic, I'd like to request it be added to gonic. This is particularly helpful for users with songs that do not use the Latin alphabet, as the sort name will be the closest equivalent in the Latin alphabet.

My chief desire is to be able to search for artists using the sort name, which I would hope could be as simple as adding another conditional in search3.

The metadata tag name is typically "artistsort". There also exists "albumartistsort", which is likely worth adding at the same time.

I will be honest - I am not sure if the actual 'sorting' part is done server side or client side; if it is server side, I suspect a proper implementation would require dealing with this as well.

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Thank you for the consideration and thank you so much for this project! If you agree with the change and could give your thoughts on implementation, I will happily look into preparing a PR.