Add mavlink support for GIMBAL_DEVICE_INFORMATION

[cmic0]

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Describe problem solved by this pull request

gimbal_device_information message has quite some fields like gimbal vendor, model and firmware version that become very important when operators need to check which firmware version/model is currently installed on the gimbal.
The only way to propagate this information to the GCS is by requesting the message when the GCS connects to the autopilot, however in the current implementation PX4 would not forward the message.

Looking at the protocol (https://mavlink.io/en/services/gimbal_v2.html) seems that this case was not taken into consideration, but on the other hand the message definition states that "This message should be requested by the gimbal manager or a ground station using MAV_CMD_REQUEST_MESSAGE (https://mavlink.io/en/messages/common.html#GIMBAL_DEVICE_INFORMATION).

another option would be to include the GIMBAL_DEVICE_INFORMATION into the GIMBAL_MANAGER_INFORMATION.
@julianoes, what do you think about the above?

Describe your solution

Allow forwarding GIMBAL_DEVICE_INFORMATION when requested

Describe possible alternatives

A clear and concise description of alternative solutions or features you've considered.

Test data / coverage

How was it tested? What cases were covered? Logs uploaded to https://review.px4.io/ and screenshots of the important plot parts.

Additional context

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[julianoes]

I think this works but alternatively PX4 could also copy the info of the device into the manager message. Doesn't that work?

[cmic0]

I think this works but alternatively PX4 could also copy the info of the device into the manager message. Doesn't that work?

Yes that would work but we'd need to extend the GIMBAL_MANAGER_INFORMATION to include the new fields

[julianoes]

Yes that would work but we'd need to extend the GIMBAL_MANAGER_INFORMATION to include the new fields

Feel free 😄

[cmic0]

For the sake of keeping entropy low, i'd just stick with allowing forwarding the GIMBAL_DEVICE_INFORMATION when requested, which would make it work as described in "This message should be requested by the gimbal manager or a ground station using MAV_CMD_REQUEST_MESSAGE"

[cmic0]

let's get this in if no further objections :)

[tstastny]

@julianoes is this acceptable as is for now? we can look at follow up after unblocking the current form (e.g. looking into directly forwarding the mavlink message after receiving from gimbal - @cmic0 was not successful in getting this to work so far)

[julianoes]

@julianoes is this acceptable as is for now?

Not sure. Do you really need the vendor information etc. for a gimbal that is integrated via PWM and not a MAVLink gimbal by itself? If you really need that then I guess this is acceptable.

[tstastny]

I guess in the case that PX4 has "its own" gimbal, e.g. a PWM one, it would have to fake the gimbal device message as you suggest in this PR.

approving and merging in current form accordingly to unblock this case

unblocking operations now, can implement alternate approach in follow up once figured out how