feat/fix: support .yaml extension for the config file.

[aloysb]

@hywax

After a little bit of pain setting mafl today I thought I would propose this PR.
I took me a little bit of digging to find out that I named my config config.yaml instead of config.yml.

Since .yaml is the official extension for yaml file, we should probably support it :)

Goal

Support .yaml extension (as well as .yml) for the config
.yaml is the official extension, but since all the docs points to .yml I don't think we should enforce it as the default or only option. But supporting config.yaml seems important.

Besides, the unraid is currently pointing to a config.yaml which would result in an error!

How to test

There isn't a test suite as far as I can tell (happy to set one up for you) so I didn't put any tests - only manually checked the code.

To do, run this branch locally with a config.yaml and ensure it works as expected!

Thanks for the good work, I love this project.

[hywax-assistant]

👋 @aloysb

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