cli: add garage json-api command and fix cargo tests

src/garage/cli/remote/mod.rs

@@ -108,21 +108,15 @@ impl Cli {
 	}
 
 	pub async fn cmd_json_api(&self, endpoint: String, payload: String) -> Result<(), Error> {
-		use std::io::Read;
-
-		let payload_json = if payload == "-" {
-			let mut buf = String::new();
-			std::io::stdin().read_to_string(&mut buf)?;
-			buf
+		let payload: serde_json::Value = if payload == "-" {
+			serde_json::from_reader(&std::io::stdin())?
 		} else {
-			payload
+			serde_json::from_str(&payload)?
 		};
-		let payload: serde_json::Value = serde_json::from_str(&payload_json)?;
 
-		let payload = serde_json::json!({
+		let request: AdminApiRequest = serde_json::from_value(serde_json::json!({
 			endpoint.clone(): payload,
-		});
-		let request: AdminApiRequest = serde_json::from_value(payload)?;
+		}))?;
 
 		let resp = match self
 			.proxy_rpc_endpoint