Get classic inverter status

[cengelen]

Summary
Add support for retrieving classic inverter config data, for instance status. Having this data the Growatt component in Home Assistant can also show if a classic inverter is on or off. Also made some improvements in the documentation and running the example file.

What this PR does:

• Adds a implementation to fetch classic inverter information.
• Improves the settings example interaction for plant/device selection to make testing easier.
• Expands documentation and examples for update_classic_inverter_setting.

Checklist

• I've made sure the PR does small incremental changes. (new code additions are dificult to review when e.g. the entire repository got improved codestyle in the same PR.)
• I've added/updated the relevant docs for code changes i've made.

[cengelen]

Hi @indykoning, do you mind taking a look?

[indykoning]

This is now available in 2.1.0 🚀