Allow conditional creation of metrics server APIService

[GusAntoniassi]

Use-Case

We are using an implementation based on external-metrics-multiplexer to be able to use KEDA alongside kube-metrics-adapter, to allow a more phased out migration of our scaling workloads to KEDA.

Currently, there is no way to disable the creation of KEDA's v1beta1.external.metrics.k8s.io APIService in this chart. The only flag in apiservice.yaml is metricsServer.enabled, however we still need the metricsServer deployment for this multiplexer scenario.

Specification

• Add value metricsServer.createApiService (bool, default true) to gate only the APIService creation

Proposed change

In templates/metrics-server/apiservice.yaml:

- {{- if .Values.metricsServer.enabled }}
+ {{- if and .Values.metricsServer.enabled (.Values.metricsServer.createApiService | default true) }}

Defaulting to true via | default true preserves existing behavior for all users.

[omkar619-dev]

Hey @GusAntoniassi ,
I'd like to pick this up, if nobody else is on it.

One note on the proposed diff — .Values.metricsServer.createApiService | default true won't actually work, because Go templates treat false as empty, so false | default true evaluates to true and the flag can never be turned off. I confirmed this with helm template. Declaring createApiService: true in values.yaml and using the value directly gives correct behaviour in all cases while preserving the existing default.

Also worth pairing in the docs: with the APIService not created, certificates.operator.apiServicePatching.enabled should be set to false as well (added in #832), otherwise the operator's cert rotator still targets an APIService that doesn't exist.

Related prior art: #443 attempted this in 2023 but was closed because the author's own use case (two KEDA installs per cluster) turned out to be unworkable — the feature itself was never objected to.

[omkar619-dev]

@GusAntoniassi bumping this — still happy to take it if it's free. The | default true issue I mentioned is the only thing I'd want confirmed before opening a PR, since it changes whether the flag is declared in values.yaml or left to the template.