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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_timestamp(ax, time=None, x=0.99, y=-0.04, ha='right', high_contrast=False, pretext='Created: ', time_format='%Y-%m-%dT%H:%M:%SZ', **kwargs):
 """Add a timestamp to a plot. Adds a timestamp to a plot, defaulting to the time of plot creation in ISO format. Parameters ax : `matplotlib.axes.Axes` The `Axes` instance used for plotting time : `datetime.datetime` Specific time to be plotted - datetime.utcnow will be use if not specified x : float Relative x position on the axes of the timestamp y : float Relative y position on the axes of the timestamp ha : str Horizontal alignment of the time stamp string high_contrast : bool Outline text for increased contrast pretext : str Text to appear before the timestamp, optional. Defaults to 'Created: ' time_format : str Display format of time, optional. Defaults to ISO format. Returns ------- `matplotlib.text.Text` The `matplotlib.text.Text` instance created """

    if high_contrast:
        text_args = {'color': 'white',
                     'path_effects':
                         [mpatheffects.withStroke(linewidth=2, foreground='black')]}
    else:
        text_args = {}
    text_args.update(**kwargs)
    if not time:
        time = datetime.utcnow()
    timestr = pretext + time.strftime(time_format)
    return ax.text(x, y, timestr, ha=ha, transform=ax.transAxes, **text_args)