feat: impl Default for RemoteClientBuilder

[danbev]

This commit adds an implementation of the Default trait for RemoteClientBuilder.

The motivation for this is that there is currently a clippy warning about this being generated:

$ cargo clippy
Checking seedwing-policy-engine v0.1.0
(/seedwing/seedwing-policy/engine)
warning: you should consider adding a `Default` implementation for
`RemoteClientBuilder`
  --> engine/src/client.rs:28:5
   |
28 | /     pub fn new() -> Self {
29 | |         let builder = reqwest::ClientBuilder::new();
30 | |
31 | |         #[cfg(not(target_arch = "wasm32"))]
...  |
38 | |         Self { client }
39 | |     }
   | |_____^