CI improvements

Some improvements to CI:

• Use ci-templates from FDO
• Add merge-request/commit checks from ci-fairy
• Add aarch64 build/tests (a bit flaky atm)
• Add another static analysis task for clang's scan-build

Other changes have been left aside atm:

• macos and windows builds. We are unable to pull all of our dependencies via meson subprojects, so that requires us to brew/pacman a whole bunch of stuff every time. Might be nice (if possible) to have pre-built images there too
• I added an asan build, but removed it. It's just as flaky as aarch, and it got too confused about sqlite memory usage, so the output when it did succeed wasn't that much useful either.