Baro offset calibration based on GNSS height

[haumarco]

Solved Problem

Account for baro offset between GNSS heigth and baro height from very beginning. Store it as offset, since its not a bias but a "fixed" value from the start.

Solution

When vehicle is still on the ground, GNSS-height gets fused and GNSS is selected as the height reference (EKF2_HGT_REF) then the baro pressure offset gets adjusted to match the GNSS height.

Test coverage

Tested on hardware

[github-actions]

🔎 FLASH Analysis

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--------------  -------------- 
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px4_fmu-v6x [Total VM Diff: 712 byte (0.04 %)]

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--------------  -------------- 
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Updated: 2025-05-27T15:29:53

[bresch]

Minor comments, otherwise good to go!