add help option on archiver plugin

[sebsto]

add a --help option to the archiver plugin

Motivation:

The only way to know what available options are was to look at the code

Modifications:

Add a swift package archive --help command line option to print a descriptive help text

Result:

$ swift package archive --help                                 

OVERVIEW: A SwiftPM plugin to build and package your lambda function.

REQUIREMENTS: To use this plugin, you must have docker installed and started.

USAGE: swift package --disable-sandbox archive [--help] [--verbose]
                                           [--output-directory <path>]
                                           [--products <list of products>]
                                           [--configuration debug | release]
                                           [--swift-version <version>]
                                           [--base-docker-image <docker_image_name>]
                                           [--disable-docker-image-update]
                                          

OPTIONS:
--verbose                     Produce verbose output for debugging.
--output-directory <path>     The path of the binary package.
                              (default is `.build/plugins/AWSLambdaPackager/outputs/...`)
--products <list>             The list of executable targets to build.
                              (default is taken from Package.swift)
--configuration <name>        The build configuration (debug or release)
                              (default is release)
--swift-version               The swift version to use for building. 
                              (default is latest)
                              This parameter cannot be used when --base-docker-image  is specified.
--base-docker-image <name>    The name of the base docker image to use for the build.
                              (default : swift-<version>:amazonlinux2)
                              This parameter cannot be used when --swift-version is specified.
--disable-docker-image-update Do not attempt to update the docker image
--help                        Show help information.

[sebsto]

The Swift Format error is not on the new code from this PR, it is on LambdaRuntime.swift
To be fixed in a separate PR

diff --git a/Sources/AWSLambdaRuntimeCore/LambdaRuntime.swift b/Sources/AWSLambdaRuntimeCore/LambdaRuntime.swift
index f36c7ee..908e2ab 100644
--- a/Sources/AWSLambdaRuntimeCore/LambdaRuntime.swift
+++ b/Sources/AWSLambdaRuntimeCore/LambdaRuntime.swift
@@ -14,15 +14,15 @@

[fabianfett]

Let's try to get rid of --disable-sandbox in #379.

[sebsto]

Agree, but this is another subject. I'll have separate PRs to address these two changes.

Can we first merge this one ?