`build-container-image` help should include all the options supported by `containertool`

The plugin help only reports arguments which are specific to the plugin and refers the reader to `containertool`. This is unhelpful because `containertool` is not the main interface for most users. The plugin's help text should describe all options.

```
% swift package build-container-image --help
Plugin ‘ContainerImageBuilder’ wants permission to allow all network connections on all ports.
Stated reason: “This command publishes images to container registries over the network”.
Allow this plugin to allow all network connections on all ports? (yes/no) yes
Building for debugging...
[1/1] Write swift-version-1AF32027EA501FB9.txt
Build of product 'containertool' complete! (3.26s)
USAGE: build-container-image

OPTIONS
--product Product to include in the image

Other arguments are passed to the containertool helper.
```

```
% swift run containertool --help
[1/1] Planning build
Building for debugging...
[1/1] Write swift-version-1AF32027EA501FB9.txt
Build of product 'containertool' complete! (3.36s)
OVERVIEW: Build and upload a container image

USAGE: containertool [] --repository

ARGUMENTS:
Executable to package

OPTIONS:
--default-registry
Default registry for references which do not specify a registry (default: docker.io)
--repository
Repository path
--resources Resource bundle directory
--username Username
--password Password
-v, --verbose Verbose output
--allow-insecure-http
Connect to the container registry using plaintext HTTP (values: source, destination, both)
--architecture
CPU architecture
--from Base image reference (default: swift:slim)
--os Operating system (default: linux)
--tag Tag for this manifest
--enable-netrc/--disable-netrc
Load credentials from a netrc file (default: --enable-netrc)
--netrc-file
Specify the netrc file path
-h, --help Show help information.
```
Ideally this would be possible without having to duplicate the help text.

Start by comparing the `swift package build-container-image --help` and `swift run containertool --help` entry points shown in the issue, then trace where each command assembles its help output. Done means the plugin help exposes all supported `containertool` options without requiring users to consult the helper and avoids duplicating the help text where possible.

Written by the indexing model from the issue text.