Draft: Add macOS support

This MR contains Bindings.xcframework build manually from client repo, using the following script:

go mod tidy
rm -rf vendor/
go build ./...
go get golang.org/x/mobile/bind
go install golang.org/x/mobile/cmd/gomobile@latest
gomobile init
gomobile bind -target ios,iossimulator,macos gitlab.com/elixxir/client/bindings

go version go1.17.13 darwin/arm64