fix: set environment variables config values correctly for camelCaseconfig keys

[doxsch]

Lowercase the keys that are stored internally within Koanf and reload them. This is a workaround because internally keys are stored case sensitive. This causes the problem that environment variables can't match the exact key and therefore will not be unmarshalled as expected anymore.

Same workaround as in redpanda console: https://github.com/redpanda-data/console/blob/a0408520cedfdd73f4f444ddbfd364faceeb0b5f/backend/pkg/config/config.go#L162-L177

closes #179