Add extraObjects value that allows creating supportive / adhoc resources

[colearendt]

Is your feature request related to a problem? Please describe.
Yes. On first deployment of the couchdb helm chart, I need to create the adminSecret myself

Describe the solution you'd like
There is a pattern I have recently been made aware of in helm charts to create an extraObjects value, evaluated as a template (similar to discussion on traefik/traefik-helm-chart#588 ), which allows deploying supporting kubernetes resources along with the traefik deployment.

In many cases, it can avoid the need for additional (fake helm chart w/ a few resources), extended (chart that extends the couchdb chart), or adhoc deployments (kubectl apply and friends).

We discussed before adding to our helm charts here: rstudio/helm#115

I'm not sure if Bitnami deserves the original credit, but they call their value extraDeploy. We thought extraObjects was a better name in our context 🤷

In any case, I would be happy to write a PR with the functionality if it seems like a welcome addition. In particular, we would use it immediately for:

• deploying the secret
• supportive prometheus, certificate, etc. deployment

Our implementation:
https://github.com/rstudio/helm/blob/ac2ad2b2e3c84309a456f6229934e5170c82164e/charts/rstudio-library/templates/_tplvalues.tpl#L6-L14

https://github.com/rstudio/helm/blob/ac2ad2b2e3c84309a456f6229934e5170c82164e/charts/rstudio-connect/templates/extra-objects.yaml#L1-L4

Describe alternatives you've considered
Create secret manually, wrap this helm chart into another, or create a little "secret" helm chart that just deploys the secret

Additional context

[pierluigilenoci]

FYI helm/helm#12653