[Feature]: Metadata download option(s)

[good-pm]

Checklist

• I searched existing issues first.
• This request fits Sake as an open-source self-hosted reading stack.

What problem are you trying to solve?
Manually searching for metadata outside of Sake is time-consuming.

Which part of Sake would this affect?

• Web app
• API
• KOReader plugin
• Sync/progress/device flow
• Search/download providers
• Self-hosting / deployment
• Documentation
• Something else

What would you like to see?
Metadata downloader with multiple providers to choose from - Amazon, Hardcover, ISBN, etc.

Why is this valuable?
Some books do not download with much metadata. This feature would:

1. Fetch metadata on download and/or
2. Offer a metadata search for books already in the library

Alternatives or workarounds
The alternative now is to manually search for metadata and add/update it field-by-field.

Additional context
Calibre-Web-Automated offers an excellent metadata fetch/update feature set. I'm sure other apps (especially Calibre-based) offer something similar, but it's the only one I have have used.

[Sudashiii]

I am working on it but it takes some time, since im kinda busy right now. @good-pm

[Sudashiii]

Okay the PR(s) is mostly done. I kinda refactored how fetching metadata works. It is now a bit more abstract and new metadata providers can easily be added in code.

The current available providers are Google, OpenLibrary (both were already available) and Hardcover (new) (technically also I wrote the code for isbnDB but they have no free tier, so it is not tested and i also did not mention it in the readme).

If you have any new metadata providers, adding them should be faster now, just create a new feature request.

[good-pm]

Is Refetch the right way to trigger this or is there some other way to pick/understand where the metadata is being pulled from? If I have multiple providers enabled, how do I know which is being used?