fix: include write_api in python sample code

[robberthofmanfm]

Closes #

When copying from the Python samples (influxdb-endpoint/orgs/org/load-data/client-libraries/python), Option 2 (data point) and Option 3 (batch sequence) do not include the definition of write_api as of now, so Python will complain.

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[wiedld]

@robberthofmanfm -- apologies on the delay. If you wouldn't mind rebasing your branch, I'll re-trigger the CI and we'll hopefully get this merged!