Add support for layered and plugin configurations (#1543)

- This adds support for reading configurations from
  a three layer hierarchy:
  1. User provided TOML
  2. Install root TOML
  3. Code defaults
- We add some code to support plugin configurations
  via the ConfigurationLoader. Each plugin can provide
  a struct with an accompanying id that gets used to
  parse the scoped section of the TOML.

Sources/ContainerCommands/Container/ContainerCreate.swift

@@ -56,7 +56,7 @@ extension Application {
         var arguments: [String] = []
 
         public func run() async throws {
-            let containerSystemConfig: ContainerSystemConfig = try ConfigurationLoader.load()
+            let containerSystemConfig: ContainerSystemConfig = try await ConfigurationLoader.load()
             let progressConfig = try ProgressConfig(
                 showTasks: true,
                 showItems: true,

Sources/ContainerCommands/Container/ContainerRun.swift

@@ -63,7 +63,7 @@ extension Application {
         var arguments: [String] = []
 
         public func run() async throws {
-            let containerSystemConfig: ContainerSystemConfig = try ConfigurationLoader.load()
+            let containerSystemConfig: ContainerSystemConfig = try await ConfigurationLoader.load()
             var exitCode: Int32 = 127
             let id = Utility.createContainerID(name: self.managementFlags.name)