Support `extraEnv` in helm chart

[attilakreiner]

Is your feature request related to a problem? Please describe.
Using the env variable in the values.yaml requires some unusual quoting in some cases (e.g. numeric values have to be double quoted like '"42"'); other helm charts use a different implementation which results in easier usage. This could be implemented by adding support for an extraEnv variable without introducing a breaking change.

Describe the solution you'd like
We should implement an extraEnv variable in the values.yaml for more natural quoting syntax when providing values for environment variables in the Deployment definition.

Describe alternatives you've considered
n/a

Additional context
For example:

env:
  - name: PORT
    value: '"42"'

vs

extraEnv:
  - name: PORT
    value: "42"