Database for telemetry readings

[oscgonfer]

This is a proof of concept PR to be elaborated further, but featuring a small database for telemetry. The idea is to create something similar to: https://docs.smartcitizen.me/hardware/firmware/?h=flash#flash-storage

The database contains a set of records in memory, ideally (although not working yet) encoded to protobuf and writable to the FS. This would allow to:

• Retrieve average/min/max readings for telemetry with admin commands
• Store delivery status, enforcing retries for certain roles (SENSOR) in which telemetry is interesting
• Serve as a backup ifor storing data to an sd-card later on (with additional flags)

Current implementation relies on a protobuf definition implemented in meshtastic/protobufs#854
This is simply a PoC, not sure it's a good idea. If moving forward, it'd require work on:

• Make sure writing / reading works to FS.
• Writing can be done per GROUPS, keeping a separate index for the currently used group, to avoid writing / reading big groups every time.
• Improvements to recover data from storage to MQTT for certain roles (SENSOR), to avoid gaps in received packets.

This is currently disabled by default and needs: #define MESHTASTIC_EXCLUDE_AIR_QUALITY_DB 0

🤝 Attestations

• I have tested that my proposed changes behave as described.
• I have tested that my proposed changes do not cause any obvious regressions on the following devices:
  • Seeed Studio ESP32-S3 (partially)