Use minreq instead of reqwest

[aumetra]

The latest version of utoipa-swagger-ui introduced a dependence on reqwest at build-time just to download a single file.

That feels unnecessarily heavy, considering it's intended to be a one-off download thing, and reqwest pulls in the entirety of hyper, tokio, mio, and all supporting libraries of that.

This PR replaces it with minreq which has a smaller dependency tree.
The difference here is that minreq buffers the entire body into memory, but I checked the size of the archive and 4MB seem like a fine amount to buffer in memory.

If it isn't, then we can switch to ureq which offers an io::Read based interface, so it streams the response (but it is a little heavier on dependencies than minreq, but not by much).

[juhaku]

I am not fond to accept a crate as a dependency that is not licensed either with MIT or Apache-2.0 or both of them. Also as what comes to the functionalities it is unfortunate that using async rust based crate bring a lot of dependencies. However like the reqwest crate https://docs.rs/reqwest/latest/reqwest/#proxies, the library should support proxies, more over the system proxies that are set with HTTP_PROXY and HTTPS_PROXY environment variables. This is fundamental because some people might be working from within corporation network that is behind a VPN where all the internet traffic is routed through a custom HTTP(S) proxy. If the crate does not support these by default then those users will face frustration when they cannot build their crates.

[aumetra]

That would then be ureq. Is MIT/Apache Dual licensed and can read proxies from the environment.

Just one sidenote: the fact that anything is downloaded here at all breaks building this crate via Nix since you can't just access the network while Nix builds a crate, since that would potentially break reproducibility.

[juhaku]

Just one sidenote: the fact that anything is downloaded here at all breaks building this crate via Nix since you can't just access the network while Nix builds a crate, since that would potentially break reproducibility.

Yeah related to that there is ongoing discussion here #923.