Updates for release v21.09.

[tenthirtyam]

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Summary of Pull Request

• Added support for Microsoft Windows Server 2022 machine image builds.
• Refactored configuration files to be generated using templates. Reduces the number of files and passes variables into the .pkrtpl.hcl content.
• Refactored builds for Linux distributions to use http_content instead of http_directory and http_file.
• Refactored builds for Microsoft Windows to use cd_content instead of floppy_files, which allows for use generated configuration files. A Packer compatible .iso command-line tool is required and noted in the README.md.
  ->>> * Refactored configuration files for Linux distributions - packages, comments, and CIS benchmarks.
• Added disclaimers and updated descriptions in script files.
• Added NOTICE.
• Updated the packer init commands run in build.sh.
• Updated MAINTAINERS.md.
• Updated CONTRIBUTING.md.
• Updated README.md.

Type of Pull Request

• This is a bug fix.
• This is an enhancement or feature.
• This is a code style / formatting update.
• This is a documentation update.
• This is a refactoring update.
• This is a something else.
  Please describe:

Context of the Pull Request

• Added support for Microsoft Windows Server 2022 machine image builds.
• Refactored configuration files to be generated using templates. Reduces the number of files and passes variables into the .pkrtpl.hcl content.
• Refactored builds for Linux distributions to use http_content instead of http_directory and http_file.
• Refactored builds for Microsoft Windows to use cd_content instead of floppy_files, which allows for use generated configuration files. A Packer compatible .iso command-line tool is required and noted in the README.md.

Related to Existing Issues

Issue Number: None

Test and Documentation Coverage

• Tests have been been completed (for bug fixes / features).
• Documentation has been added / updated (for bug fixes / features).

Breaking Changes?

• Yes, there are breaking changes.
• No, there are no breaking changes.

[github-actions]

I'm going to lock this pull request because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues. If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.