Changed draw_geometries to use default args instead of overload

[timohl]

Type

• Bug fix (non-breaking change which fixes an issue): Fixes #
• New feature (non-breaking change which adds functionality). Resolves #
• Breaking change (fix or feature that would cause existing functionality to not work as expected) Resolves #

Motivation and Context

Currently, o3d.visualization.draw_geometries uses overloading to provide default values for lookat, up, front, and zoom.
This causes two problems:

• It defines a function with default arguments before non-default arguments (forbidden by The Python Language Reference)
• It clutters the documentation with redundancy (see docs/0.18.0/python_api/open3d.visualization.draw_geometries)

Checklist:

• I have run python util/check_style.py --apply to apply Open3D code style
  to my code.
• This PR changes Open3D behavior or adds new functionality.
  • Both C++ (Doxygen) and Python (Sphinx / Google style) documentation is
    updated accordingly.
  • I have added or updated C++ and / or Python unit tests OR included test
    results (e.g. screenshots or numbers) here.
• I will follow up and update the code if CI fails.
• For fork PRs, I have selected Allow edits from maintainers.

Description

This PR uses utility::optional to provide a single binding function (no overload) with a clean argument list.
The arguments are in line with the cpp implementation (which also uses default args).
This solution avoids named args before positional args.

This is a fix used in #6917 since mypy would complain about non-default argument follows default argument [syntax].

[update-docs]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.

[ssheorey]

Looks good. Thanks @timohl !