[WIP] [Request] Add support for intermediate meter to measure the outputpower of the inverter

[Copilot]

Adding support for an intermediate meter to measure inverter output power for Dynamic Power Limiter functionality.

Plan:

• Analyze existing PowerMeter system architecture
• Understand how PowerLimiter uses power meter data
• Examine configuration structures and Web API patterns
• Create InverterMeter system similar to PowerMeter but for measuring inverter output
• Add configuration structures for InverterMeter
• Implement InverterMeter controller following PowerMeter pattern
• Integrate InverterMeter with PowerLimiter for faster inverter output readings
• Add Web API endpoints for InverterMeter configuration
• Test integration with PowerLimiter functionality

Changes Made:

• Added InverterMeter controller that reuses PowerMeter providers
• Added InverterMeter configuration structures to Configuration.h
• Integrated InverterMeter with PowerLimiter for faster readings when available
• Modified PowerLimiter to skip waiting for new power meter readings when InverterMeter provides recent data
• Modified PowerLimiter to use InverterMeter total power reading instead of summing individual inverter outputs when available
• Added Web API endpoints for InverterMeter configuration
• Added serialization/deserialization for InverterMeter configuration

This enables users to configure a separate meter (like Shelly EM) to measure inverter output power directly, providing faster and more reliable readings than waiting for DTU statistics for the Dynamic Power Limiter functionality.

Fixes #899.

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[rradkov]

I think this is a great future that I'm waiting for so long... Just want to add a hint here. There are cases(like mine) that two inverters HMS-2000 and HMS-1000 are connected to the same intermediate meter - Shelly 1 PM so please include this type of case as well.

[AndreasBoehm]

@rradkov Using a intermediate meter for multiple inverters defeats the purpose of this feature. The idea behind the feature is that we don't trust the inverters ac output value because it might be wrong or not really up to date. If you use the same meter for multiple inverters we still can't do anything with the measurements besides displaying them.