NBSNEBIUS-89: [Tasks] support 'crontab' parameters for regular tasks

[SvartMetal]

Support crontab-like params for regular tasks.
Example:

  ...
  // Schedules one task at 19:30 of each day.
  s.scheduler.ScheduleRegularTasks(
    ctx,
    "regular",
    tasks.TaskSchedule{
      MaxTasksInflight: 1,
      UseCronTab:       true,
      Hour:             19,
      Minute:           30,
    },
  )

[qkrorlqr]

Если хочется, чтобы либу активно использовали, надо для каждой новой фичи писать хотя бы минималистичную документацию с примером использования

[github-actions]

Note

This is an automated comment that will be appended during run.

🟢 linux-x86_64-relwithdebinfo: all tests PASSED for commit f6db9b3.

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
4700	4628	0	0	0	72