[JENKINS-1255] Add support of @reboot, et al. cron extensions #24101

On Debian, cron offers:

@​reboot Run once, at startup.
@​yearly Run once a year, "0 0 1 1 *".
@​annually (same as @​yearly)
@​monthly Run once a month, "0 0 1 * *".
@​weekly Run once a week, "0 0 * * 0".
@​dailyRun once a day, "0 0 * * *".
@​midnight (same as @​daily)
@​hourly Run once an hour, "0 * * * *".

several of which may be generally. cF issue 680

On Debian, cron offers:

@reboot       Run once, at startup.
@yearly       Run once a year, "0 0 1 1 *".
@annually     (same as @yearly)
@monthly      Run once a month, "0 0 1 * *".
@weekly       Run once a week, "0 0 * * 0".
@daily        Run once a day, "0 0 * * *".
@midnight    (same as @daily)
@hourly       Run once an hour, "0 * * * *".

several of which may be generally. cF issue 680

• environment: Platform: All, OS: All