fix WriteToBigTable DirectRow

[aIbrahiim]

fixes #30760, fixes #34990

google-cloud-bigtable 2.44 changed DirectRow and PostCommit test_bigtable_write started to fail so the driver uses 2.44 and workers still use 2.42, so pickle loses _pb_mutations

The PR fills _pb_mutations before pickle and before write so old workers can still write the rows

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[github-actions]

Assigning reviewers:

R: @damccorm for label python.
R: @igorbernstein2 for label bigtable.

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[Amar3tto]

Tested: https://github.com/apache/beam/actions/runs/34204205571

[Abacn]

cc: @mutianf (for Bigtable client breaking change)

Also we should regenerate Python requirement, especially bump this line:

beam/sdks/python/container/py310/base_image_requirements.txt

Line 67 in c4cfdef

google-cloud-bigtable==2.42.0

should fix the issue. cc: @shunping ( regenerate Python requirement then release a new beam-master image)

[shunping]

I didn't know there would be an issue on pickling here. How about we just bump the lower bound of bigtable?

Then we can also simplify the current code to only support bigtable>=2.44

[aIbrahiim]

@Abacn thanks, I can bump bigtable to >=2.44.0 in setup.py and drop the pickle fix

@shunping would you regenerate the Python container requirements and publish a new beam-master image so workers get 2.44 too?

[shunping]

Sure. We can help generate the new beam image.