- `HEALTH_OPENVPN_DURATION_INITIAL` renamed to `HEALTH_VPN_DURATION_INITIAL` with retro-compatiblity
- `HEALTH_OPENVPN_DURATION_ADDITION` renamed to `HEALTH_VPN_DURATION_ADDITION` with retro-compatiblity
- No more global variables
- Inject merged servers to configuration package
- Fix#566: configuration parsing to use persisted servers.json
- Move server data files from `internal/constants` to `internal/storage`