add koel-init to do init tasks and add the flags to the docs,

[AEnterprise]

Right now you can't deploy koel in docker without manual intervation, this pr resolves that by automatically running koel:init (as non interactive), as well as koel:doctor to report the status. If no config is present it will just "start" but not work as before until the user provides/mounts a valid .env file

However the big difference is now that once this config file exists, koel can self-update and no longer needs manual intervention. the init and doctor output during startup also makes it easier to diagnose issues for users unfamiliar with the koel inner workings. This behavior is on by default but can be disabled with the SKIP_INIT flag

side note: smtp not being configured is currently an "error", this should probably be a warning since it work just fine without

This script can also optimize the config loading, since it has some pitfals for unaware users (requiring a config reboot to apply) i've left this off by default and needs the OPTIMIZE_CONFIG to apply. While needing a reboot to apply config changes is fairly standard in docker containers, i didn't want to break current behavior. Maybe could be enabled by default in a later major release?