Add support for updating classic inverter settings

[cengelen]

Summary

This pull request introduces a new function, update_classic_inverter_setting, to the GrowattApi class. This function allows users to apply settings to classic inverters, expanding the library's functionality to support more inverter types, like the older MTL-S series.

Additionally, a new example script, settings_example_classic.py, has been added to demonstrate how to use this function. The documentation in shinephone.md and inverter_settings.md has also been updated to include details about the new function.

Motivation

• The addition of update_classic_inverter_setting addresses the need for my legacy/classic inverter, which was previously not covered by the library. Using this function I can enable/disable the inverter based on dynamic energy rates.

Checklist

• I've made sure the PR does small incremental changes. (The new function, example script, and documentation updates are isolated changes.)
• I've added/updated the relevant docs for code changes I've made. (Documentation in shinephone.md and inverter_settings.md has been updated.)

[cengelen]

Hi @indykoning,
Please check this small PR so I can use this in the Home Assistant integration.

I think this would be beneficial for a lot of people using older Growatt inverters and dynamic tariffs.
Thank you!