Adapt https://github.com/aya-rs/aya/commit/3d463a3 and subsequent work
to the template. This has worked very well for us in the main project,
and our users should get the same hotness.
Add a new command to build ebpf and userspace programs without running.
```
cargo xtask build
```
Co-authored-by: Michal Rostecki <vadorovsky@protonmail.com>
The default log level of env_logger is `error`. We are using `info!` in
the template, so let's suggest running the example with `RUST_LOG=info`.
Signed-off-by: Michal Rostecki <vadorovsky@gmail.com>