Support fetching tracker list from URL

[Piccirello]

This feature is adapted from qBittorrent-Enhanced-Edition to allow for automatically adding trackers retrieved from a URL. @ngosang's trackerlist repo is a good example, however I've opted not to include a default URL.

Partially addresses #14535.

[thalieht]

I see only 1 problem: The box for Automatically append these trackers to new downloads is now too short in GUI, it was 8 lines high and now it's 4.5 (on my machine).

[stalkerok]

Supersedes? #20115

[Piccirello]

I see only 1 problem: The box for Automatically append these trackers to new downloads is now too short in GUI, it was 8 lines high and now it's 4.5 (on my machine).

In my testing, the height is unchanged compared to master on linux and v5.0.0 on macOS.

Supersedes? #20115

Ah yes - I hadn't noticed that PR. These seem to be based off of the same original code.

[stalkerok]

Tested! Did not test WebUI.

[ngosang]

I maintain https://github.com/ngosang/trackerslist since 8 years ago and I will keep maintaining it. It's used by several opensource projects. I have been contributor of qBittorrent long time ago too. You can add it as default if you want to.

https://github.com/ngosang/trackerslist/graphs/contributors

[Piccirello]

I maintain https://github.com/ngosang/trackerslist since 8 years ago and I will keep maintaining it. It's used by several opensource projects. I have been contributor of qBittorrent long time ago too. You can add it as default if you want to.

https://github.com/ngosang/trackerslist/graphs/contributors

The reason I opted not to include a default tracker list was due to potential legal concerns. If this isn't an issue, I can use your list. (cc @qbittorrent/lead-developers)

[stalkerok]

I think adding a default link is not a good idea. Everyone uses different services with a list of trackers, I use https://newtrackon.com/.

[Chocobo1]

Seems you don't really need this since you already have m_additionalTrackerEntriesFromURL.

[Piccirello]

This is mostly useful for the comparison against the existing tracker list to determine if we need to call populateAdditionalTrackersFromURL(), though it's also used to get the list of trackers to display. We could instead do the comparison against QList<TrackerEntry> m_additionalTrackerEntriesFromURL and parse this every time, but it seemed easier to keep around the QString.