fix: LSDV-5071: Ensure secret key is securely set persisting a new one if required (#4690)

* feat: retrieve SECRET_KEY from env with fallback

* fix: LSDV-5071: Ensure secret key is securely set persisting a new one if required

* use the ls data dir env if specified with a fallback to the standard directory location

* add more context to warning message

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Co-authored-by: Robert Schuh <github@eneticum.de>