Improved the Build subcommand to support the building of Docker images (#11)

This PR contains the work done to support the building of Docker images in the `Build` subcommand in the executable target. So, for this purpose, the following task have been done:

- added a basic boilerplate of the `docker-compose.yml` file;
- fixed some issues found in the boilerplate of the `Dockerfile` file;
- defined the `Randomable` protocol;
- defined the `Artifact` enumeration;
- updated the `BuildProjectTask` task to support building Docker images if required;
- renamed the `BuildProjectTask` task as `BuildArtifactTask`.

Reviewed-on: #11
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Library/Sources/Internal/Enumerations/File.swift

@@ -2,6 +2,7 @@ enum File: String {
     case appArguments = "AppArguments"
     case appBuilder = "AppBuilder"
     case appOptions = "AppOptions"
+    case dockerCompose = "DockerCompose"
     case dockerFile = "DockerFile"
     case dockerIgnore = "DockerIgnore"
     case environment = "Environment"
@@ -24,6 +25,7 @@ extension File {
         case .appArguments: "AppArguments.swift"
         case .appBuilder: "AppBuilder.swift"
         case .appOptions: "AppOptions.swift"
+        case .dockerCompose: "docker-compose.yml"
         case .dockerFile: "Dockerfile"
         case .dockerIgnore: ".dockerignore"
         case .environment: "Environment+Properties.swift"