allow empty status informers

[cbodonnell]

What this PR does / why we need it:

This PR allows an empty array of status informers to be explicitly passed to the SDK. Previously if this was the case, the SDK would automatically generate status informers based on the Helm release. The default value for statusInformers will still result in them being automatically generated, which maintains existing behavior.

Which issue(s) this PR fixes:

Part of https://app.shortcut.com/replicated/story/88171/detect-and-configure-the-replicated-sdk-chart-subchart-if-it-s-part-of-the-vendor-s-application

Special notes for your reviewer:

Steps to reproduce

Does this PR introduce a user-facing change?

Status informers will no longer be automatically generated if the user explicitly passes an empty array for the `statusInformers` value.

Does this PR require documentation?

NONE

[sgalsaleh]

nit pick: any reason not to use --set replicated.statusInformers=[]?

[cbodonnell]

that ended up rendering this:

statusInformers:
  - "[]"

[sgalsaleh]

huh, that's not what Helm's docs say. It's fine then, let's leave it as is.

https://helm.sh/docs/intro/using_helm/#the-format-and-limitations-of---set

[cbodonnell]

saw that too. maybe it's because of how we template it

$ helm template replicated chart/replicated-0.0.0.tgz --set statusInformers=[] | grep -i statusInformers -A1
    statusInformers:
      '[]'

[sgalsaleh]

yeah, probably. hmm, this might break in a production install if someone decides to override status informers using helm set, right?

[cbodonnell]

if they try to override it using --set replicated.statusInformers=[]

[cbodonnell]

the key issue is that {{- if .Values.statusInformers }} evaluates to true when using --set replicated.statusInformers=[], but evaluates to false when passing the same via a user-provided values file. looking like Helm is interpreting [] as a string in the former case and as an array in the latter.

[sgalsaleh]

Why not use if not (kindIs "invalid" ... like we do with the integration.enabled field?

[cbodonnell]

The result is the same in that case as it's interpreted as a string when --set replicated.statusInformers=[] is passed to the cli:

$ helm template replicated chart/replicated-0.0.0.tgz --set statusInformers=[] | grep -i statusInformers -A1
    statusInformers:
      '[]'