ci: Build darwin tag builds on linux

[camscale]

Build the tag builds of the terraform provider and event-handler for
darwin on linux. These are pure Go programs so can easily be
cross-compiled using GOOS/GOARCH. The "tricky" part is the universal
binary, solved by using https://github.com/konoui/lipo - a Go version of
lipo (the tool that constructs universal binaries) that can run on
Linux.

[wadells]

I've tested this at:

• terraform https://drone.platform.teleport.sh/gravitational/teleport-plugins/3012/2/4
• event handler https://drone.platform.teleport.sh/gravitational/teleport-plugins/3011/3/1

Both look good.

I downloaded the universal terraform binary and checked it on my mac, as well as the amd64 eventhandler plugin:

walt@work plugins % ./teleport-event-handler/teleport-event-handler version
Teleport event handler v14.0.0 go1.21.1
walt@work plugins % ./terraform-provider-teleport version                  
This binary is a plugin. These are not meant to be executed directly.
Please execute the program that consumes these plugins, which will
load any plugins automatically

[camscale]

Closing this in favour of #922