Update all references of the new command in docs

Signed-off-by: Min Kim <minkimcello@gmail.com>

docs/plugins/backend-plugin.md

@@ -10,18 +10,12 @@ Backstage repository.
 ## Creating a Backend Plugin
 
 A new, bare-bones backend plugin package can be created by issuing the following
-command in your Backstage repository root:
+command in your Backstage repository root and selecting `backend-plugin`:
 
 ```sh
-yarn new --select backend-plugin
+yarn backstage-cli new
 ```
 
-Please also see the `--help` flag for the `new` command for some
-further options that are available, notably the `--scope` and `--no-private`
-flags that control naming and publishing of the newly created package. Your repo
-root `package.json` will probably also have some default values already set up
-for these.
-
 You will be asked to supply a name for the plugin. This is an identifier that
 will be part of the NPM package name, so make it short and containing only
 lowercase characters separated by dashes, for example `carmen`, if it's a

docs/plugins/create-a-plugin.md

@@ -15,9 +15,11 @@ invoking the
 from the root of your project.
 
 ```bash
-yarn new --select plugin
+yarn new
 ```
 
+And then select `frontend-plugin`.
+
 ![Example of output when creating a new plugin](../assets/getting-started/create-plugin_output.png)
 
 This will create a new Backstage Plugin based on the ID that was provided. It

docs/plugins/integrating-plugin-into-software-catalog.md

@@ -21,7 +21,8 @@ should have a separate package in a folder, which represents your plugin.
 Example:
 
 ```
-$ yarn new --select plugin
+$ yarn new
+# Select `frontend-plugin`
 > ? Enter an ID for the plugin [required] my-plugin
 > ? Enter the owner(s) of the plugin. If specified, this will be added to CODEOWNERS for the plugin path. [optional]