feat: implement service type NodePort

[lucasl0st]

This PR adds support for Kubernetes services of type NodePort.
I tried my best to keep the structure of the configuration and code the same as for the LoadBalancer service type.

If the configuration for the NodePort is enabled the LoadBalancer configuration is overwritten.
Specific ports to be used on the kubernetes node(s) can be specified, if left empty kubernetes picks a port based on the clusters configuration: https://kubernetes.io/docs/concepts/services-networking/service/#type-nodeport

Implements #983
Probably supersedes #994

Since this is my first PR at Zalando and this repository, please feel free to let me know if you would like me to make changes, if you want a specific test or if I need to bump a version somewhere. Thank you!

[zalando-robot]

Cannot start a pipeline due to:

No accountable user for this pipeline: no Zalando employee associated to this GitHub username

Click on pipeline status check Details link below for more information.

[zalando-robot]

Cannot start a pipeline due to:

No accountable user for this pipeline: no Zalando employee associated to this GitHub username

Click on pipeline status check Details link below for more information.

[zalando-robot]

Cannot start a pipeline due to:

No accountable user for this pipeline: no Zalando employee associated to this GitHub username

Click on pipeline status check Details link below for more information.

[zalando-robot]

Cannot start a pipeline due to:

No accountable user for this pipeline: no Zalando employee associated to this GitHub username

Click on pipeline status check Details link below for more information.

[zalando-robot]

Cannot start a pipeline due to:

No accountable user for this pipeline: no Zalando employee associated to this GitHub username

Click on pipeline status check Details link below for more information.

[zalando-robot]

Cannot start a pipeline due to:

No accountable user for this pipeline: no Zalando employee associated to this GitHub username

Click on pipeline status check Details link below for more information.

[FxKu]

@lucasl0st sorry for the delay reviewing you nice contribution. This looks like the best attempt so far to get NodePort service type support in our operator. I've checked most changes briefly so far and it looks sound.

On general implementation detail we need to think about is what takes precedence when both NodePort and LoadBalancer service type are enabled from the manifest or config? I think this should create an LB, maybe with a hard-coded port if NodePort is specified in the manifest. In the pooler code, for example, I saw that you added NodePort configuration after the LB.