FMT-75 Add hook for packer fmt

[godotgildor]

Description

Creates a hook for running packer fmt similar to the hook for running terraform fmt.

resolves #75

Documentation

Updated README.md to describe the new hook.

TODOs

Please ensure all of these TODOs are completed before asking for a review.

• [ X] Ensure the branch is named correctly with the issue number. e.g: feature/new-vpc-endpoints-955 or bug/missing-count-param-434.
• [ X] Update the docs.
• [X ] Keep the changes backward compatible where possible.
• [ ?] Run the pre-commit checks successfully.
• [X ] Run the relevant tests successfully.
• [ X] Ensure any 3rd party code adheres with our license policy or delete this line if its not applicable.

Related Issues

NA

[godotgildor]

Any questions, suggestions, or concerns @brikis98 or @yorinasub17 ?

[godotgildor]

@brikis98 or @yorinasub17 - any update on this PR?

[godotgildor]

@brikis98 or @yorinasub17 - any chance to get a quick review on this? I think having a packer fmt hook would be a nice addition.