Provide uncertainty frequency example using framecpp.py

Need to provide a pure framecpp python exmple for uncertainty channel:

This example shows how to do it using lal and lalframe

import numpy

import lal
import lalframe

from gwpy.frequencyseries import FrequencySeries



# generate fake data
data = FrequencySeries(
    numpy.random.random(16384),
    df=.5,
    name="TEST",
    unit="m",
    epoch=1234567890,
)

# write to GWF using LALFrame
frame = lalframe.FrameNew(
    epoch=data.epoch.gps,
    duration=4,
    project="LIGO",
    run=4,
    frnum=0,
    detectorFlags=lal.LHO_4K_DETECTOR_BIT|lal.LLO_4K_DETECTOR_BIT,
)
lalframe.FrameAddREAL8FrequencySeriesProcData(
    frame,
    series=data.to_lal(),
    subtype=6,
)
lalframe.FrameWrite(frame, "test.gwf")