[Spotify] Audiobook support

[jonnynews]

Not a bug, but a feature request. Spotify announced audiobook support back in March 2024. This would be great in owntone supported audiobooks, like it support podcasts.

[jonnynews]

Seems similar to the work done on podcast in #1286 by @chme.

There seems to be apis present for audiobooks

https://developer.spotify.com/documentation/web-api/reference/get-an-audiobook
https://developer.spotify.com/documentation/web-api/reference/get-users-saved-audiobooks

Should not be the hard to put in.

[hacketiwack]

Yes, I think it is a very reasonable feature to ask.
I will check the API and keep you posted.

[hacketiwack]

I looked a wee bit more into it.
Problem is now that the currently used Spotify library is quite outdated. Last version was released 4 years ago.
I'll probably have to switch to another library, like the official one.

[jonnynews]

The official library seems to support audiobooks. See this.

BTW, I am developer, I don't know your codebase super well, but I am help out with code review and testing. Not written C in a while, but I write javascript / typescript everyday.

[hacketiwack]

Thanks @jonnynews.
I will check how to properly do the authentication with the official API and keep you posted about my progress.