Add support for standalone yamlfix config files

[JP-Ellis]

Description

In addition to support configuration within pyproject.toml, add support for a standalone yamlfix.toml or .yamlfix.toml file.

Additional context

When Yamlfix is used as part of a Python project, it is fantastic to have the config within the central pyproject.toml file; however, not all projects are Python projects.

I think it would be really nice if Yamlfix provided support for both .yamlfix.toml and yamlfix.toml.

Related Issue

This is related to:

• Read configuration file from a default predefined location #233

Though the above differs in that I am suggesting a per-project configuration, as opposed to a global user config.

Implementation

If that is something that would be desirable, it seems like it should be rather trivial to implement using the existing maison framework: https://maison.readthedocs.io/en/latest/usage.html#source-files. I would be happy to contribute a PR.