Automatically trigger ebpf build on cargo run in workspace root

[tomaszjonak]

Poked a little today but no satisfying results. Looks like this would be a clean solution rust-lang/cargo#9096. It is not stabilized yet though.

[vadorovsky]

An another problem is that the ebpf crate has to be built with -Z build-std=core argument. I don't think that the current bindep solution supports providing rustc flags for a single crate inside workspace.

https://github.com/deepfence/guardity/blob/main/xtask/src/build_ebpf.rs#L49-L50

We tried to think many times how could we drop the build-ebpf xtask, but there is no way to make it work now.

https://discord.com/channels/855676609003651072/855676609003651075/1014674111475241082
https://discord.com/channels/855676609003651072/855676609003651075/872750358231928833