Add AI query skill + adding support for changing default fallback skill

[tylxr59]

This is kind of a big addition, hopefully it's up to snuff.

Added in the AI query skill - It defaults to OpenAI's endpoint and gpt-4o-mini but is compatible with any provider that uses an OpenAI-style API. It does require that the end user have an funded/paid account with an API provider to function. I'm happy to provide maintainers a short-term key for testing.

I also added in a new Settings menu entry to allow users to select a default fallback skill when the input is not recognized as a command. By default, it still does the "I couldn't understand you, please try again" behavior but can be changed to the AI query.

I do find that the translate skill does clash with the AI query skill - sometimes queries meant for the AI get picked up by the translation skill. I, personally, just disabled the translation skill and have found using ChatGPT's translations to be alright.

I haven't changed the README but I would be more than happy to supply a How-To section for setting it up and acquiring API keys.

Resolves https://github.com/Stypox/dicio-android/issues/366 (partially), https://github.com/Stypox/dicio-android/issues/132