Add top level clustering field

[nrfox]

Adds a top level clustering field to the kiali spec.

Relates to kiali/kiali#6243

[jmazzitelli]

Need to do 2 things:

1. You should remove the deprecated feature flags from values.yaml.

2. Then you need to change the templates to use these new settings:

So you will want to change this stuff:

• https://github.com/kiali/helm-charts/blob/v1.78.0/kiali-server/templates/_helpers.tpl#L181-L182
• https://github.com/kiali/helm-charts/blob/v1.78.0/kiali-server/templates/deployment.yaml#L134
• https://github.com/kiali/helm-charts/blob/v1.78.0/kiali-server/templates/deployment.yaml#L177

You can see all these places that use the feature flags via:

$ grep -R "kiali_feature_flags.clustering" *
templates/_helpers.tpl:{{- if .Values.kiali_feature_flags.clustering.autodetect_secrets.enabled }}
templates/_helpers.tpl:  {{- $secretLabelToLookFor := (regexSplit "=" .Values.kiali_feature_flags.clustering.autodetect_secrets.label 2) }}
templates/deployment.yaml:        {{- range .Values.kiali_feature_flags.clustering.clusters }}
templates/deployment.yaml:      {{- range .Values.kiali_feature_flags.clustering.clusters }}

This is the server helm chart (provided for convienence) so we are less strict about backwards compatibility. We will, however, make a note of this in the release notes so people are aware of this change. cc @jshaughn (he produces the release notes).