Add args to enable passing input to resource export

[SteveL-MSFT]

PR Summary

Missing args to dsc to enable passing input to direct resource export. Created export test resource to validate.

PR Context

Fix #678

[Copilot]

PR Overview

This pull request adds support for passing input arguments to the resource export functionality and includes test coverage for the new export command.

• Adds a new Export struct and related tests in dsctest.
• Updates command-line argument parsing and resource command handling to accept and process export input.
• Integrates the export command in both the testing tool and the main DSC CLI.

Reviewed Changes

File	Description
tools/dsctest/src/export.rs	Introduces the Export struct with a count field for testing.
tools/dsctest/src/main.rs	Implements export subcommand handling with JSON input parsing.
tools/dsctest/src/args.rs	Adds export command support via Clap arguments.
dsc/src/args.rs	Updates resource export arguments to include input and file options.
dsc/src/subcommand.rs	Modifies export subcommand dispatch to process input via get_input.
dsc/src/resource_command.rs	Updates the export function to accept and process the input JSON.

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (2)

tools/dsctest/src/main.rs:74

• [nitpick] Consider rephrasing the error message for clarity, for example: 'Error: Export input JSON does not match expected schema: {err}'.

eprintln!("Error JSON does not match schema: {err}");

dsc/src/resource_command.rs:217

• [nitpick] Consider exiting the process after the adapter resource is not found (instead of returning) to maintain consistency with other error handling in resource commands.

error!("{}: {requires}", t!("resource_command.adapterNotFound")); return;