K2V client improvements (#307)

- [x] Better distinguish error types
- [x] Parse error messages received from server
- [x] Remove `src/` folder layer, we don't have that for other crates

Co-authored-by: Alex Auvolat <alex@adnab.me>
Reviewed-on: https://git.deuxfleurs.fr/Deuxfleurs/garage/pulls/307
Co-authored-by: Alex <alex@adnab.me>
Co-committed-by: Alex <alex@adnab.me>

src/k2v-client/error.rs

@@ -0,0 +1,29 @@
+use std::borrow::Cow;
+
+use thiserror::Error;
+
+/// Errors returned by this crate
+#[derive(Error, Debug)]
+pub enum Error {
+	#[error("{0}, {1}: {2} (path = {3})")]
+	Remote(
+		http::StatusCode,
+		Cow<'static, str>,
+		Cow<'static, str>,
+		Cow<'static, str>,
+	),
+	#[error("received invalid response: {0}")]
+	InvalidResponse(Cow<'static, str>),
+	#[error("not found")]
+	NotFound,
+	#[error("io error: {0}")]
+	IoError(#[from] std::io::Error),
+	#[error("rusoto tls error: {0}")]
+	RusotoTls(#[from] rusoto_core::request::TlsError),
+	#[error("rusoto http error: {0}")]
+	RusotoHttp(#[from] rusoto_core::HttpDispatchError),
+	#[error("deserialization error: {0}")]
+	Deserialization(#[from] serde_json::Error),
+	#[error("{0}")]
+	Message(Cow<'static, str>),
+}