Add bin directory for oak_loader

[ipetr0v]

This change adds a binary directory for oak_loader.

Fixes #719
Originated from #1214 (comment)

Checklist

• Pull request includes prototype/experimental work that is under
  construction.

[ipetr0v]

If we will compile oak_loader in bin, do we need to run it from there?
Or we should still use cargo run ...?
cc @anghelcovici @tiziano88

[tiziano88]

If we will compile oak_loader in bin, do we need to run it from there?
Or we should still use cargo run ...?
cc @anghelcovici @tiziano88

I feel we should stop using cargo run and bazel run at some point, it's not very realistic of how the binaries are normally run. So I vote for building first, and then running as binary later. Happy to hear other opinions though.