Move RCON_ENABLED from scripts/functions expect start.sh to RCON function

[Dashboy1998]

Is your feature request related to a problem? Please describe.
Currently we check RCON_ENABLED in many places

Describe the solution you'd like
Ideally only need to check if RCON is enabled in the RCON function and start.sh.

Describe alternatives you've considered
None

Additional context
RCON function returns the exit code of the rcon-cli command. Check it in the RCON function and return 1 if RCON_ENABLED is not true.