Added multistage build for Dockerfile

[danielsagi]

Description

Until now we used alot of unnecessary alpine packages in the final image. Now we only use the site-packages directory and the kube-hunter installed binary on a python alpine base image

Fixed Issues

This removes vulnerabilities found in kube-hunter image. as well as reduce size from 300MB~ to 77MB!

Contribution checklist

• [x] I have read the Contributing Guidelines.
• [ ] The commits refer to an active issue in the repository.
• [ ] I have added automated testing to cover this case.

Notes

Please mention if you have not checked any of the above boxes.

[codecov[bot]]

Codecov Report

Merging #362 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #362   +/-   ##
=======================================
  Coverage   62.77%   62.77%           
=======================================
  Files          42       42           
  Lines        2281     2281           
=======================================
  Hits         1432     1432           
  Misses        849      849           

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[danielsagi]

@itaysk , Right, historically we installed them to remove warnings when loading scapy. in my tests I actually haven't seen warnings. But I added them again, seems to me that we will need them. the important part is removing the build packages.