fix(services) support non-None ClusterIP always

[rainest]

What this PR does / why we need it:

Support user-chosen ClusterIP values for all Service types so long as the ClusterIP value is not the special "None" value.

Support the "None" value when the Service type is ClusterIP.

Which issue this PR fixes

https://github.com/Kong/charts/pull/961#pullrequestreview-1765916969

Special notes for your reviewer:

Examples:

$ helm template ana /tmp/symkong --set admin.enabled=true --set admin.clusterIP=None --set admin.type=NodePort 2>/dev/null | grep -i clusterIP:
$ helm template ana /tmp/symkong --set admin.enabled=true --set admin.clusterIP=None --set admin.type=ClusterIP 2>/dev/null | grep -i clusterIP:
  clusterIP: None
$ helm template ana /tmp/symkong --set admin.enabled=true --set admin.clusterIP=10.0.0.1 --set admin.type=ClusterIP 2>/dev/null | grep -i clusterIP: 
  clusterIP: 10.0.0.1
$ helm template ana /tmp/symkong --set admin.enabled=true --set admin.clusterIP=10.0.0.1 --set admin.type=NodePort 2>/dev/null | grep -i clusterIP: 
  clusterIP: 10.0.0.1
$ helm template ana /tmp/symkong --set admin.enabled=true --set admin.type=NodePort 2>/dev/null | grep -i clusterIP: 
$ helm template ana /tmp/symkong --set admin.enabled=true --set admin.type=ClusterIP 2>/dev/null | grep -i clusterIP: 

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• [x] PR is based off the current tip of the main branch.
• [x] Changes are documented under the "Unreleased" header in CHANGELOG.md
• [x] New or modified sections of values.yaml are documented in the README.md
• [x] Commits follow the Kong commit message guidelines