Enable backtracing for images created with the plugin

Include swift-backtrace-static, from the swift static SDK, alongside the binary when it's copied into the container in order to allow the container to capture stack traces on a crash and report them.

I'm tempted to ask for a way to set a default environment variable (SWIFT_BACKTRACE) on the container as well, but the permutations get large for the [docs of that feature](https://github.com/swiftlang/swift/blob/main/docs/Backtracing.rst), and that can be set at runtime as well, so I'm not certain it's nearly as critical as just enabling the binary to capture the stack traces.

Start by tracing the plugin's step that copies the built binary into the container and check how dependencies from the Swift static SDK are selected. Confirm how swift-backtrace-static should be packaged alongside the binary, then verify that a generated container can capture and report stack traces after a crash.

Written by the indexing model from the issue text.