Add feature gate support to helm chart

[thefirstofthe300]

It would be really nice if the Helm chart supported feature gates. Currently, there is no way to inject a custom env value into the chart manifest so feature gates are essentially non-operable.

[jbperrin88]

This feature is also wanted here ;p
We would like to add proxy settings via Env variable to the manager deployement for pgo

[benjaminjb]

Sounds reasonable to me to have a way to add env vars to the Helm chart -- I'm making a ticket in our backlog for it, but I'd also welcome a PR if anyone wants to take a swing at it.