refactor!: migrate to libcurl

[Octol1ttle]

This pull request migrates* Prism Launcher's networking operations from Qt Network to libcurl.

This PR affects a lot of code due to noticeable refactoring required for various reasons.

Things left to do:

• [x] Multipart upload
• [x] Enhanced failure dialog
• [x] Proxy support
• Testing:
  • [ ] Windows
  • [ ] macOS
  • [ ] Linux

* - OAuth2 operations use Qt NetworkAuth, which relies on Qt Network. Rolling our own OAuth2 implementation is outside the scope of this PR

[txtsd]

Why do we need this?

[Octol1ttle]

Why do we need this?

It decreases Prism's reliance on Qt, which, from what I read in development channels on Discord, causes plenty of bugs in Prism, especially in networking