feat: automatically set dns service address

[prometherion]

Closes #468, pinging the main stakeholder such as @kvaps and the IPv6 gurus @johannwagner @hexchen

When defining a different Service CIDR and an empty DNS Service one, Kamaji will automatically compute the correct value.

Once applying this Tenant Control Plane snippet:

  networkProfile:
    serviceCidr: 10.20.0.0/16
    port: 6443

This is the resulting one stored in the cluster.

  networkProfile:
    clusterDomain: cluster.local
    dnsServiceIPs:
    - 10.20.0.10
    podCidr: 10.244.0.0/16
    port: 6443
    serviceCidr: 10.20.0.0/16

Tested also with IPv6:

  networkProfile:
    serviceCidr: 2002::1234:abcd:ffff:c0a8:101/64
    port: 6443

Defaulted values:

    version: v1.30.0
  networkProfile:
    clusterDomain: cluster.local
    dnsServiceIPs:
    - 2002::1234:abcd:ffff:c0a8:111
    podCidr: 10.244.0.0/16
    port: 6443
    serviceCidr: 2002::1234:abcd:ffff:c0a8:101/64

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[johannwagner]

Hey, thanks a lot for this fix.
The IPv6 given service CIDR look wrong, I would expect something like 2001:db8:abcd:efgh::/64 as CIDR with 2001:db8:abcd:efgh::10 as DNS IP.

[prometherion]

Are you sure the 2001:db8:abcd:efgh:: address is correct? I'm getting a network validation error.

Also, I'm a bit confused: why 10 instead of a? If I understood correctly, the octet is way bigger in IPv6, so 010 in IPv4 would be translated into 000a in IPv6.

Ok, maybe I'm getting your point: in IPv4 we can expect a +10 bit in the last octet, and +16 in IPv6?

[johannwagner]

Whoopsie, I fucked up the example. 2001:db8:abcd::/64 is correct. The other one also has host bits set, which is not correct.

I guess so, they specify :10 as DNS address, which is 16 bits added to the network address.

[prometherion]

Thanks, I added the required changes, such as:

• adding 10 bit for IPv4
• adding 16 bits for IPv6

I updated the initial comment on the issue just for reference.