service: launch only once

[NickHackman]

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This change adds a MacOS launchctl configuration to services that allows providing the LaunchOnlyOnce boolean flag.

     LaunchOnlyOnce <boolean>
     This optional key specifies whether the job can only be run once and only once.  In other words, if the job cannot be safely
     respawned without a full machine reboot, then set this key to be true.

NOTE: this is MacOS only, if there's a way to provide this for systemd that'd be awesome!

Issue: abiosoft/colima#96

[SMillerDev]

Where did you get the documentation from? I can't find that option in https://www.launchd.info/ or https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/Introduction.html

CC @carlocab

[carlocab]

man launchd.plist:

     LaunchOnlyOnce <boolean>
     This optional key specifies whether the job can only be run once and only once.  In other words, if the job cannot be safely
     respawned without a full machine reboot, then set this key to be true.

[SMillerDev]

Additionally, I think Type=oneshot would be the systemd equivalent.

[MikeMcQuaid]

Thanks so much for your first contribution to Homebrew! Without people like you submitting PRs we couldn't run this project. You rock, @NickHackman!