[FEATURE] Adjust task delay duration before first call

[lqmanh]

Is your feature request related to a problem? Please describe.
For now, repeat_every decorator only allows us to delay the first call exactly 1 interval with wait_first set to True. We can't do things like wait for 1 minute, then execute the task every 1 hour.

Describe the solution you'd like
Make wait_first accept an int argument.

@repeat_every(seconds=3600, wait_first=60)
def foo():
    """Wait for 60s, then execute this once per hour."""

@repeat_every(seconds=3600, wait_first=True)
def bar():
    """Wait for 1 hour, then execute this once per hour."""

[jkklapp]

Im happy to take this one