Add extraArgs config for kube-router

[jnummelin]

Description

This is for advanced use cases and users that need to control things like ASN, routing and peering. Allows also users to override any k0s managed startup args.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

• Manual test
• Auto test added

Checklist:

• My code follows the style guidelines of this project
• My commit messages are signed-off
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

[AskAlice]

a bit confused, why would this fail validation?

          kubeRouter:
            autoMTU: true
            hairpin: "Enabled"
            extraArgs:
              - peer-router-ips="172.16.0.1,172.16.1.1"
              - peer-router-asns=64512,64512
              - cluster-asn=64512

or as an object

            extraArgs:
             	peer-router-ips: "172.16.0.1,172.16.1.1"
                peer-router-asns: 64512,64512
                cluster-asn: 64512

edit: ahh it's because they all need to be strings, even if they're really uint or array

            extraArgs:
              peer-router-ips: "172.16.0.1,172.16.1.1"
              peer-router-asns: "64512,64512"
              advertise-cluster-ip: "true"
              advertise-external-ip: "true"
              advertise-loadbalancer-ip: "true"
              cluster-asn: "64512"
              ```

[AskAlice]

this is not a valid flag and causes kube-router to error if this property is defined

[twz123]

Not sure what you're referring to? The additionalProperties stuff is OpenAPI-specific and not referring to actual kube-router flags.