Add option to create parent folders when copying files or folders to Windows containers

[wbpascal]

Description

This PR adds a boolean option windows_create_parent_dirs to the plugin config with a default value of false (for backwards compatibility). When this value is true, the parent folders of the destination are created within the Windows container during copying of files or folders into a Windows container. This makes the behavior closer to the way it works for Linux containers currently and also helps when reusing Packer files between VMs (e.g., utilizing the vSphere plugin) and containers (using this plugin).

For more context, please also see #208.

Resolved Issues

Closes #208

Rollback Plan

If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

There are no changes to security controls in this PR.

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[Copilot]

Pull request overview

This PR introduces a new Docker builder configuration option, windows_create_parent_dirs, to optionally create missing destination parent directories when uploading files/directories into Windows containers, aligning behavior more closely with Linux container uploads.

Changes:

• Added windows_create_parent_dirs to the Docker builder config/schema with docs and changelog updates.
• Implemented parent-directory creation in the Windows container communicator prior to Copy-Item operations.
• Added config validation warning behavior and unit tests covering defaulting and warnings.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
docs/builders/docker.mdx	Documents the new option and shows it in Windows container examples.
docs-partials/builder/docker/Config-not-required.mdx	Adds the option to the generated config reference list.
CHANGELOG.md	Notes the new feature under “Unreleased”.
builder/docker/windows_container_communicator.go	Adds parent-dir creation logic for Windows uploads (and related helpers).
builder/docker/config.hcl2spec.go	Extends HCL2 spec to include windows_create_parent_dirs.
builder/docker/config.go	Adds config field and emits a warning if set without windows_container.
builder/docker/config_test.go	Adds tests for default value and warning behavior.

Files not reviewed (1)

• builder/docker/config.hcl2spec.go: Language not supported

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