Add minimal proxy capabilities to dioxus serve

This adds an MVP of some proxying capabilities to the `dioxus serve`
server. The config is similar to that of `trunk serve`: the user can
specify one or more proxy backends under `[[web.proxy]]` in Dioxus.toml,
and the server will intercept requests targeted at the _path_ of that
configured backend and forward them to the backend server.

Example
-------

For example, if the dev server is serving on port 8080 with this config:

```
[[web.proxy]]
backend = "http://localhost:9000/api"
```

then requests to http://localhost:8080/api,
http://localhost:8080/api/ and http://localhost:8080/api/any-subpath
to be forwarded to the respective paths on http://localhost:9000.

This PR doesn't handle path rewriting or anything yet but it would be
fairly simple to add in future if anyone needs it.

Cargo.lock

@@ -715,6 +715,7 @@ dependencies = [
  "headers",
  "html_parser",
  "hyper",
+ "hyper-rustls",
  "indicatif",
  "lazy_static",
  "log",
@@ -1329,7 +1330,9 @@ checksum = "1788965e61b367cd03a62950836d5cd41560c3577d90e40e0819373194d1661c"
 dependencies = [
  "http",
  "hyper",
+ "log",
  "rustls",
+ "rustls-native-certs",
  "tokio",
  "tokio-rustls",
 ]
@@ -2330,6 +2333,18 @@ dependencies = [
  "webpki",
 ]
 
+[[package]]
+name = "rustls-native-certs"
+version = "0.6.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0167bac7a9f490495f3c33013e7722b53cb087ecbe082fb0c6387c96f634ea50"
+dependencies = [
+ "openssl-probe",
+ "rustls-pemfile",
+ "schannel",
+ "security-framework",
+]
+
 [[package]]
 name = "rustls-pemfile"
 version = "1.0.2"