last_data_received_at should be based on last sent PM sensor data

[karimkawambwa]

Description

Sometimes the sensor stops sending PM data but keeps sending humidity/temperature values and therefore we miss the PM data. This PR makes a change to prioritize caching of last received based on the PM data.

Fixes # (issue)

Type of change

• [x] New feature (non-breaking change which adds functionality)

Checklist:

• [ ] My code follows the style guidelines of this project
• [ ] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation

[karimkawambwa]

👍 @karimkawambwa

Thinking out loud, shouldn't there be a limit to this? I mean if a sensor hasn't send PM data in 3 months while we're still receiving temp & humidity data, should we still report that the last time we received data from this node was 3 months ago?

@kilemensi I think that will probably deserve another variable to track. Thanks for raising that issue, I will plan to add that variable incase its needed or that case happens. (aka for debug purposes)