Firmware metadata autoupdate

[dagar]

As configuration complexity continues to increase and become more board specific we need to ensure parameter metadata is as up to date as possible. To simplify the metadata download I'd like to upload per-board, per-version XML files.

Then QGC would need to automatically download if necessary.

Example: http://px4.aws.com/meta/<product_id>/<git_hash>.xml where product_id and git_hash come from the MAVLink AUTOPILOT_VERSION packet (which is already in QGC).

We should also review other issues around parameter metadata update during flashing. It oftens seems to get stuck and refuse to take new metadata from the .px4 binary.

PX4/PX4-Autopilot#10337 (comment)
PX4/PX4-Autopilot#9615 (comment)