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

[euanh]

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>

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 [<options>] --repository <repository> <executable>

ARGUMENTS:
  <executable>            Executable to package

OPTIONS:
  --default-registry <default-registry>
                          Default registry for references which do not specify a registry (default: docker.io)
  --repository <repository>
                          Repository path
  --resources <resources> Resource bundle directory
  --username <username>   Username
  --password <password>   Password
  -v, --verbose           Verbose output
  --allow-insecure-http <allow-insecure-http>
                          Connect to the container registry using plaintext HTTP (values: source, destination, both)
  --architecture <architecture>
                          CPU architecture
  --from <from>           Base image reference (default: swift:slim)
  --os <os>               Operating system (default: linux)
  --tag <tag>             Tag for this manifest
  --enable-netrc/--disable-netrc
                          Load credentials from a netrc file (default: --enable-netrc)
  --netrc-file <netrc-file>
                          Specify the netrc file path
  -h, --help              Show help information.

Ideally this would be possible without having to duplicate the help text.

[euanh]

One option would be to include --product in containertool as a non-functional argument for compatibility with the plugin. The plugin's help could then delegate to containertool --help, possibly overriding the executable name.

[euanh]

Alternatively, the plugin help is just a fixed string. The plugin could execute containertool --help and insert its own --product option as the first argument after OPTIONS:.

[euanh]

Variation on option 1: containertool help includes --product (and any other plugin options) when a special environment variable or hidden option is specified.