Microservice versioning Proof of Concept

[AmeliaEScott]

Related:

• Microservice versioning document
• Microservice Versioning Proof of Concept PX4/PX4-Autopilot#13565
• [WIP] Added documentation for experimental microservice versioning feature PX4/PX4-Devguide#945

This PR uses this common.xml, and this C library generated from it.

This is still a work in progress, because the exact API for microservice versioning has not been finalized. In addition, there is still work to be done on this code:

• Clean up old code that is currently commented out
• Determine how the mission microservice should act with systems that do not perform the microservice version handshake
• Update comments in the Mission microservice to reflect the changes
• Update MAVLink module to include new auto-generated constants for service IDs and new messages
• Thorough testing

This is currently a minimum functioning prototype. Work is now being done in PX4 and MAVSDK to reach the same state, while the specifications are finalized and MAVLink is updated.

More context: https://docs.google.com/document/d/1zK_JcJbhtbRA3W0MgnXSNWMUxOcBu6vXocrjZVMXki4/

[hamishwillee]

FWIW

Determine how the mission microservice should act with systems that do not perform the microservice version handshake

Exactly as it does before this change - ad hoc fallback.

Update MAVLink module to include new auto-generated constants for service IDs and new messages

Hmmm. The new messages need to be updated, and they can go in as WIP anytime. We hadn't actually discussed/considered generation of the services and version numbers via the toolchain. It makes sense though.

[AmeliaEScott]

Yes, I think it is important to generate constants like MAVLINK_SERVICE_ID_MISSION and so on. I don't know how the service numbers should be generated as constants. Perhaps MAVLINK_SERVICE_MISSION_MAX_VERSION or something? But that is so far less important to me.