CI observability enhancements. (#1193)

- Adds a a `--log-root` option to `swift system start`, propagating the
value as `CONTAINER_LOG_ROOT` to services for logging to files instead
of the OS log facility. This is not a "production" capability as it
neither merges nor rotates logs.
- Currently we don't collect logs on CI builds, and we don't have
permission to run the `log` command there. The PR adds `--log-root` to
the CI test phase, archives the results, and uploads the archive as an
artifact.
- Use FilePath from swift-system for the log root. Foundation URL is a
bit of a footgun for filesystem paths, so unless we identify a
showstopper, we should incrementally transition to this type everywhere
except where we really need network URLs.
- Output the hostname of the CI runner at the start of the test phase so
we can identify runner-specific issues where they exist.
- Fix formatting for log messages with multiple metadata items, and fix
unstructured messages on instances that weren't found using `grep -r
'log\.' Sources`.
- Adds command reference documentation for `--log-root`.

Sources/ContainerCommands/System/SystemStart.swift

@@ -21,6 +21,7 @@ import ContainerPlugin
 import ContainerXPC
 import ContainerizationError
 import Foundation
+import SystemPackage
 import TerminalProgress
 
 extension Application {
@@ -42,6 +43,12 @@ extension Application {
             transform: { URL(filePath: $0) })
         var installRoot = InstallRoot.defaultURL
 
+        @Option(
+            name: .long,
+            help: "Path to the root directory for log data, using macOS log facility if not set",
+            transform: { FilePath($0) })
+        var logRoot: FilePath? = nil
+
         @Flag(
             name: .long,
             inversion: .prefixedEnableDisable,
@@ -85,7 +92,12 @@ extension Application {
             var env = PluginLoader.filterEnvironment()
             env[ApplicationRoot.environmentName] = appRoot.path(percentEncoded: false)
             env[InstallRoot.environmentName] = installRoot.path(percentEncoded: false)
-
+            if let logRoot {
+                env[LogRoot.environmentName] =
+                    logRoot.isAbsolute
+                    ? logRoot.string
+                    : FilePath(FileManager.default.currentDirectoryPath).appending(logRoot.components).string
+            }
             let plist = LaunchPlist(
                 label: "com.apple.container.apiserver",
                 arguments: args,