Feature request: add FlareSolverr solver to bypass CloudFlare protection

[soredake]

Ther are a lot of sites that use cloudflare as protection, checking sites that use cloudflare can result in 403, would be nice to have support for FlareSolverr to fix this situation.

Related:
#1157
jobobby04/TachiyomiSY#1124

[mre]

First time I hear of FlareSolverr, but it looks nice. We wanted to add proxy support anyway at some point. There's a proxy config file that browsers like Firefox use. Not sure if it could also be used to call FlareSolverr.

[mre]

The proxy support request I was referring to: #869
Would it "just work" if we added support for that?

[mre]

Looks like FlareSolverr requires data to be sent as a JSON POST request? So the proxy approach wouldn't work.
There's a prototype for WebAssembly support, which could be used to modify the request. @thomas-zahner, this should work, right?

[thomas-zahner]

Yes this seems like a perfect use case of the recently implemented RequestChain. The WebAssembly part is indeed only a prototype and not merged yet. However, the request chain itself is already fully functional and available in lychee_lib through the ClientBuilder.

An example on how to make use of the RequestChain can be found here: https://github.com/lycheeverse/lychee/blob/master/examples/chain/chain.rs