cli: add service integration for macos, observability

Adds support for running the tunnel as a service on macOS via launchservices.

It also hooks up observability (`code tunnel service log`) on macOS and Linux.
On macOS--and later Windows, hence the manual implementation of `tail`--it
saves output to a log file and watches it. On Linux, it simply delegates to
journalctl.

The "tailing" is implemented via simple polling of the file size. I didn't want
to pull in a giant set of dependencies for inotify/kqueue/etc just for this use
case; performance when polling a single log file is not a huge concern.

cli/src/util/command.rs

@@ -2,10 +2,34 @@
  *  Copyright (c) Microsoft Corporation. All rights reserved.
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
-use super::errors::{wrap, WrappedError};
-use std::{ffi::OsStr, process::Stdio};
+use super::errors::{wrap, AnyError, CommandFailed, WrappedError};
+use std::{ffi::OsStr, process::Stdio, borrow::Cow};
 use tokio::process::Command;
 
+pub async fn capture_command_and_check_status(
+	command_str: impl AsRef<OsStr>,
+	args: &[impl AsRef<OsStr>],
+) -> Result<std::process::Output, AnyError> {
+	let output = capture_command(&command_str, args).await?;
+
+	if !output.status.success() {
+		return Err(CommandFailed {
+			command: format!(
+				"{} {}",
+				command_str.as_ref().to_string_lossy(),
+				args.iter()
+					.map(|a| a.as_ref().to_string_lossy())
+					.collect::<Vec<Cow<'_, str>>>()
+					.join(" ")
+			),
+			output,
+		}
+		.into());
+	}
+
+	Ok(output)
+}
+
 pub async fn capture_command<A, I, S>(
 	command_str: A,
 	args: I,