Refactor & enhance network policy reconciler

[marcrahnsap]

Description

Previously, the ksp controller and network policy reconciler were combined within a single file. Now, the reconciler is separated and the ksp controller is deleted due to the fact that we are using a different approach. There is the possibility to specify a default network policy on namespace level. This will overwrite the karydia default. This can be done by setting the namespace annotation karydia.gardener.cloud/networkPolicy.

This pull request resolves #56.

Checklist

Before submitting this PR, please make sure:

• [x] you have added unit tests
• [x] your code builds clean with make
• [x] your code lets succeed unit tests with make test
• [x] your code lets succeed integration tests

[ionysos]

@marcrahnsap: I changed solves in the description to resolves to be in accordance with Closing issues using keywords. Please keep this in mind the next time!

@marcrahnsap & @CodeClinch: If you decide to delete dependencies please remove the whole "story" not only parts of it. By chance, I've seen that there some leftovers which I thought you've already deleted. Furthermore, this led to some strange karydia behavior, figured out by @dacappo by chance, as well. I provided a new PR #102 to remove your leftovers. Please try to keep this in mind the next time!