Make the Dockerfile cross-compile without qemu

[sandhose]

This changes the Dockerfile so that it can be fully cross-compiled to arm64 & x86_64 without any qemu emulation. This should mean way less time spent building the arm64 image in CI. This also means better caching between the two architectures.

I had to bump the NAPI CLI to a 3.0 alpha version, because the new version has a handy --cross-compile flag, which automatically invokes cargo-zigbuild if needed.

[sandhose]

Thanks @AndrewFerr for the crypto SDK bindings release! I was able to remove the manual SDK download workaround 🎉

I had to upgrade via the package.json's resolutions field to override the sub-dependency, and it would require a new release of @vector-im/matrix-bot-sdk.

Also note that the upgrade does deprecate the sled store, and I have not updated the docs accordingly. What I would suggest we do is:

• release the matrix-bot-sdk with the updated bindings
• do the matrix-bot-sdk upgrade in another PR (including updates to the doc/changelog)
• I'll mark this PR as draft in the meantime, and will un-draft it once the upgrade is done