feat - images/obfsvpn/start_obfsvpn.sh - implement support to pass env for using persist conf

this will help lilypad to start obfsvpn-server with --persist true

https://0xacab.org/leap/container-platform/lilypad/-/blob/main/config/services.bitmask.yml?ref_type=heads#L121

otherwise the container was failing due to already existing keys:

Error calling ReadInConfig: Config File "obfsvpn" Not Found in "[/opt/obfsvpn]"
error while generating key:/opt/obfsvpn/data/obfs4_state.json already exists