[REVIEW] Add truncate API to python doc pages

[galipremsagar]

Description

In #11435, the truncate API was added but I had a review comment(to add it docs) that I forgot to publish. This PR adds truncate to the docs page.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[bdice]

Thanks! And sorry I missed this in my own reviews. 🤦‍♂️

[galipremsagar]

@gpucibot merge

[codecov]

Codecov Report

Base: 87.47% // Head: 88.08% // Increases project coverage by +0.61% 🎉

Coverage data is based on head (61dcf22) compared to base (f817d96).
Patch has no changes to coverable lines.

Additional details and impacted files

@@               Coverage Diff                @@
##           branch-22.12   #12109      +/-   ##
================================================
+ Coverage         87.47%   88.08%   +0.61%     
================================================
  Files               133      135       +2     
  Lines             21826    22063     +237     
================================================
+ Hits              19093    19435     +342     
+ Misses             2733     2628     -105     

Impacted Files	Coverage Δ
python/cudf/cudf/core/column/interval.py	85.45% <0.00%> (-9.10%)	⬇️
python/cudf/cudf/io/text.py	91.66% <0.00%> (-8.34%)	⬇️
python/strings_udf/strings_udf/__init__.py	76.47% <0.00%> (-7.85%)	⬇️
python/cudf/cudf/core/_base_index.py	81.28% <0.00%> (-4.27%)	⬇️
python/cudf/cudf/io/json.py	92.06% <0.00%> (-2.68%)	⬇️
python/cudf/cudf/utils/utils.py	89.91% <0.00%> (-0.69%)	⬇️
python/cudf/cudf/core/column/timedelta.py	90.17% <0.00%> (-0.58%)	⬇️
python/cudf/cudf/core/column/datetime.py	89.21% <0.00%> (-0.51%)	⬇️
python/cudf/cudf/core/column/column.py	87.96% <0.00%> (-0.46%)	⬇️
python/dask_cudf/dask_cudf/core.py	73.72% <0.00%> (-0.41%)	⬇️
... and 42 more

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