message: docs: update build system docs to use roles
diff: @@ -243,11 +243,8 @@ nevertheless be useful to know how it works, since all of the published
  Backstage packages are built using this process.
  The build is currently using [Rollup](https://rollupjs.org/) and executes in
  -isolation for each individual package. There are currently three different
  -commands in the Backstage CLI that invokes the build process, `plugin:build`,
  -`backend:build`, and simply `build`. The two former are pre-configured commands
  -for frontend and backend plugins, while the `build` command provides more
  -control over the output.
  +isolation for each individual package. The build is invoked using the `package build`
  +command, and applies to all packages roles except the bundled ones, `frontend` and `backend`.
  There are three different possible outputs of the build process: JavaScript in
  CommonJS module format, JavaScript in ECMAScript module format, and type
  @@ -281,11 +278,11 @@ cover each combination of these cases separately.
  ### Frontend Development
  -There are two different commands that start the frontend development bundling:
  -`app:serve`, which serves an app and uses `src/index` as the entrypoint, and
  -`plugin:serve`, which serves a plugin and uses `dev/index` as the entrypoint.
  -These are typically invoked via the `yarn start` script, and are intended for
  -local development only. When running the bundle command, a development server
  +The frontend development setup is used for all packages with a frontend role, and
  +is invoked using the `package start` command.
  +The only difference between the different roles is that packages with the `'frontend'`
  +role use `src/index` as the entrypoint, while other roles instead use `dev/index`.
  +When running the start command, a development server
  will be set up that listens to the protocol, host and port set by `app.baseUrl`
  in the configuration. If needed it is also possible to override the listening
  options through the `app.listen` configuration.
  @@ -309,8 +306,8 @@ support for them instead.
  ### Frontend Production
  The frontend production bundling creates your typical web content bundle, all
  -contained within a single folder, ready for static serving. It is invoked using
  -the `app:build` command, and unlike the development bundling there is no way to
  +contained within a single folder, ready for static serving. It is used when building
  +packages with the `'frontend'` role, and unlike the development bundling there is no way to
  build a production bundle of an individual plugin. The output of the bundling
  process is written to the `dist` folder in the package.
  @@ -405,7 +402,7 @@ dependencies installed, and as soon as you copy over and extract the contents of
  the `bundle.tar.gz` archive on top of it, the backend will be ready to run.
  The following is an example of a `Dockerfile` that can be used to package the
  -output of `backstage-cli backend:bundle` into an image:
  +output of building a package with role `'backend'` into an image:
  ```Dockerfile
  FROM node:16-bullseye-slim
  @@ -617,12 +614,12 @@ The following is an excerpt of a typical setup of an isomorphic library package:
  "types": "dist/index.d.ts"
  },
  "scripts": {
  - "build": "backstage-cli build",
  - "lint": "backstage-cli lint",
  - "test": "backstage-cli test",
  - "prepack": "backstage-cli prepack",
  - "postpack": "backstage-cli postpack",
  - "clean": "backstage-cli clean"
  + "build": "backstage-cli package build",
  + "lint": "backstage-cli package lint",
  + "test": "backstage-cli package test",
  + "clean": "backstage-cli package clean",
  + "prepack": "backstage-cli package prepack",
  + "postpack": "backstage-cli package postpack"
  },
  "files": ["dist"],
  ```
  