Add script to allow installation with pipx and simplify CLI usage

[pdecat]

This PR allows installation with tools like pipx:

# pipx install .
  installed package jsonata-python 0.6.0, installed using Python 3.13.3
  These apps are now globally available
    - jsonata
done! ✨ 🌟 ✨

# jsonata -h
usage: jsonata.cli [-h] [-v] [-e <file>] [-i <arg>] [-ic <arg>] [-f {auto,json,string}] [-o <arg>] [-oc <arg>] [-time] [-c] [-b <json-string>] [-bf <file>] [-it] [expr]

Pure Python JSONata CLI

positional arguments:
  expr

options:
  -h, --help            show this help message and exit
  -v, --version         show program's version number and exit
  -e, --expression <file>
                        JSON expression to evaluate.
  -i, --input <arg>     JSON input file (- for stdin)
  -ic, --icharset <arg>
                        Input character set (default=utf-8)
  -f, --format {auto,json,string}
                        Input format (default=auto)
  -o, --output <arg>    JSON output file (default=stdout)
  -oc, --ocharset <arg>
                        Output character set (default=utf-8)
  -time                 Print performance timers to stderr
  -c, --compact         Compact JSON output (don't prettify)
  -b, --bindings <json-string>
                        JSONata variable bindings
  -bf, --bindings-file <file>
                        JSONata variable bindings file
  -it, --interactive    Interactive REPL (requires input file)

Without this change:

# pipx install jsonata-python

No apps associated with package jsonata-python or its dependencies. If you are attempting to install a library, pipx should not be used. Consider using pip or a similar tool instead.

[rayokota]

Thanks @pdecat , LGTM