Improve Plugin Manager behavior

[LightDestory]

Suggestion

I would like to suggest the following improvements for the plugin manager.

1. More control over official plugin installation:

   Current behavior:
   When you check plugin updates for the first time, qBittorrent will automatically install all the official plugins.
   Suggested behavior:
   When checking for updates and if there are available not installed plugins, ask for permission to install them and let the user select which ones, with a GUI with check-boxes or similar

2. Allow unofficial plugin to use the update system:

   Current behavior:
   When you install unofficial plugins, you have to manually update them when a new update is released. You much check periodically for updates.
   Suggested behavior:
   Introduce a new keyword inside the plugin's structure like the currently used AUTHOR and VERSION. I suggest to add something like UPT-URL that contains the direct link to the plugin code to be able to re-use the check-for-update logic used for official plugins.

These changes do not introduce any conflict and will preverse backward compatibility, old qbittorrent version will just ignore UPT-URL.

I would like to work on these change but I am not very confident on my C++ to match the standard for this project. I welcome anyone that would like to tutor me while implementing such stuff, if someone expert wants to straight implement by himself I have no problems.

Thanks for your time,
LightDestory.

Use case

General use, allowing more flexibility for unofficial plugin developers.

Extra info/examples/attachments

No response

[Pentaphon]

I agree with this. I don't like how the "check for updates" button just installs all the default plugins. It should only update what is on the list and nothing more.