Build ArduPilot in CI

[spernsteiner]

This branch sets up CI to build the ArduPilot SITL binary for aarch64. Specifically, this branch adds three things:

• Build scripts for setting up the build environment and compiling the arduplane binary
• An ardupilot section in package.sh
• A CI job to build and cache the ardupilot package.

Part of #97

Checklist before requesting a review

• I have performed a self-review of my code
• My code matches the coding standards and I have ran the appropriate linters
• I included documentation updates for my code
• I extended the test suite and the tests run by the CI to cover my code
• I assigned a Milestone to this PR
• I assigned this PR to a Project
• I assigned this PR appropriate Labels

[spernsteiner]

I tested the aarch64 arduplane binary manually in the dev VM, and it worked fine - I was able to connect to it from the base system with mavproxy and run an example mission. arduplane was very slow to start up inside the nested guest VM, but once it got running, there were no issues.

[podhrmic]

LGTM