tuftool: Add --version option

[stmcginnis]

Issue #, if available:

Closes #608

Description of changes:

This adds a --version to the tuftool command to print out the tool's version number.

$ tuftool --version
tuftool 0.10.1

$ tuftool --help
This wrapper enables global options and initializes the logger before running any subcommands

Usage: tuftool [OPTIONS] <COMMAND>

Commands:
  clone              Clone a TUF repository, including metadata and some or all targets
  create             Create a TUF repository
  delegation         Delegation Commands
  download           Download a TUF repository's targets
  root               Manipulate a root.json metadata file
  transfer-metadata  Transfer a TUF repository's metadata from a previous root to a new root
  update             Update a TUF repository's metadata and optionally add targets
  help               Print this message or the help of the given subcommand(s)

Options:
  -l, --log-level <log-level>  Set logging verbosity [trace|debug|info|warn|error] [default: info]
  -h, --help                   Print help
  -V, --version                Print version

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