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 solves #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 what's with

• [ ] you have added integration tests
• [ ] you have documented new or changed features

If you're planning to add integration tests and/or document these changes, the label review wanted shouldn't be attached now. If you don't plan to add these things, the two points from the checklist should be removed because they're not applicable.

[ionysos]

@marcrahnsap, it seems that license/cla missed your PR.