Add the ability to pass environment variables in Kubernetes format

[tkukushkin]

[CLAassistant]

All committers have signed the CLA.

[kmgnd]

@kolesnikovae please note 🙏

[kolesnikovae]

Thank you for the contribution! I'd like to inform you that the repository and the helm chart are going to be depricated soon. We're going to issue our first major release – Pyroscope v1, which changes many things. In particular, the new helm chart resides in https://github.com/grafana/pyroscope/tree/next/operations/phlare