Python wrapper for OGS commandline tools

This MR adds a very simple Python wrapper for OGS commandline tools.

The usage is as follows:

$ pip install ogs

$ python
>>> from ogs import cli
>>> return_code = cli.createQuadraticMesh("--version")

.../lib/python3.10/site-packages/ogs/_internal/../bin/createQuadraticMesh  version: 6.4.3-70-gd27595c4ed

>>> outfile = "/tmp/line.vtu"
>>> return_code = cli.generateStructuredMesh(e="line", lx=1, nx=10, o=outfile)
[2022-09-29 08:05:02.718] [ogs] [info] Mesh created: 11 nodes, 10 elements.

>>> help(cli.createQuadraticMesh)
Help on function run_cmd in module ogs._internal.wrap_cli_tools:

run_cmd(*args, **kwargs)
    This function wraps the commandline tool createQuadraticMesh for easy use from Python.
    
    The entries of args are passed as is to the commandline tool.
    The entries of kwargs are transformed: one-letter keys get a single
    dash as a prefix, multi-letter keys are prefixed with two dashes.
    
    Thereby, commandline tools can be used like proper Python functions, e.g.:
    
    >>> cli = CLI()
    >>> cli.createQuadraticMesh("--help") # prints a help text
    ...
    >>> cli.createQuadraticMesh(help=None) # special, does the same
    ...
    
    A more useful example. The following will create a line mesh:
    
    >>> outfile = "line.vtu"
    >>> cli.generateStructuredMesh(e="line", lx=1, nx=10, o=outfile)

Future Work

• Improved help texts
• Autocompletion of available tools
• Options to capture tool output/write log files
• Documentation on the OGS website

Checklist

1. Feature description was added to the changelog
2. Tests covering your feature were added?
3. Any new feature or behavior change was documented?