Optimize the deepfence_agent container build

Currently building the `deepfence_agent` container image takes at least 15 minutes, regardless of how small the change is and which component or plugin was modified. That's because building the most of binaries happens in `build.sh` with `docker run` commands, like:

https://github.com/deepfence/ThreatMapper/blob/d00b722d5957f6f7a3c61294418be16b756cdcc7/deepfence_agent/build.sh#L18-L24

By doing that this way, we cannot cache any build results and builds are performed every time from scratch.

The solution for that problem is using Docker buildx multi-stage builds which will allow us to cache build artifacts for each dependency.