common: add new_mission extension to MISSION_COUNT message

[IamPete1]

This adds a extension to allow the flight controller to notify that the mission has been changed, this allows the GSC to re-load. The mission could have been changed by a second GCS, companion computer or onboard scripting.

The use case here is to deal with fences automatically set and loaded by scripting ArduPilot/ardupilot#15598

This is the demo that just streams the fence back, this is not a feasible solution IRL due to flooding the link and/or packet loss, but it shows the functionality that I would like to duplicate with this extension.
https://youtu.be/WakSwFTCeV8

[hamishwillee]

I'd rather have #1172

[IamPete1]

@hamishwillee I was not aware of that PR, as it currently stands that is for missions only so would not work for my fence use case.

No reason we cant have both, I guess that PR is not popular since it has sat for over a year?

[hamishwillee]

No reason we cant have both

I think we should try at least for just one solution, and I think the other one seems more flexible to me.

I guess that PR is not popular since it has sat for over a year?

It was essentially approved but waiting on microservices going in. Let's push it forward.

[meee1]

how does this work with packet loss? is it a single send? or until the "list" is rerequested

[IamPete1]

@meee1 Its better than my previous method of just spamming the points to GCS, At least it would now know how many points it should ask for and can re-request a point if its missing.

[hamishwillee]

As discussed in the dev call we're closing this and iterating the other item - let's make sure that does what you need Pete!