Build for mac x64 and arm64 separately and update mac deploy docs

[rly]

Ref: #309

Building separate dmg files for x64 and arm64 may not be necessary. Needs more testing, but I am caching my progress here.

See also electron-userland/electron-builder#5689 (comment)

[rly]

Update: After updating the certificates and credentials, Apple no longer complains about code signing and notarization on MacOS during the build process. Further testing needed to see whether the x64 and arm64 dmg files run correctly on their respective systems and do not trigger mac security warnings.

[CodyCBakerPhD]

Building separate dmg files for x64 and arm64 may not be necessary.

I still suspect we might need this for those handful of interfaces that struggle with M1

But this is working well for me ATM, will raise any other issues as they occur

Thanks a bunch! @rly