ARROW-15757: [Python] Missing bindings for existing_data_behavior makes it impossible to maintain old behavior

[AlenkaF]

This PR tries to pass existing_data_behavior to write_to_dataset in case of the new dataset implementation.

Connected to #12811.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-15757

[jorisvandenbossche]

Looks good!

(I did a small edit of the docstring + removed a duplicate line in there)

[ursabot]

Benchmark runs are scheduled for baseline = 916112c and contender = fed115f. fed115f is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished ⬇️0.0% ⬆️0.0%] ec2-t3-xlarge-us-east-2
[Failed] test-mac-arm
[Finished ⬇️7.86% ⬆️2.14%] ursa-i9-9960x
[Finished ⬇️0.8% ⬆️0.04%] ursa-thinkcentre-m75q
Buildkite builds:
[Finished] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-ec2-t3-xlarge-us-east-2/builds/598| fed115fd ec2-t3-xlarge-us-east-2>
[Failed] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-test-mac-arm/builds/586| fed115fd test-mac-arm>
[Finished] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-ursa-i9-9960x/builds/585| fed115fd ursa-i9-9960x>
[Finished] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-ursa-thinkcentre-m75q/builds/596| fed115fd ursa-thinkcentre-m75q>
[Finished] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-ec2-t3-xlarge-us-east-2/builds/597| 916112cf ec2-t3-xlarge-us-east-2>
[Failed] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-test-mac-arm/builds/585| 916112cf test-mac-arm>
[Finished] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-ursa-i9-9960x/builds/584| 916112cf ursa-i9-9960x>
[Finished] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-ursa-thinkcentre-m75q/builds/595| 916112cf ursa-thinkcentre-m75q>
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java

[ursabot]

['Python', 'R'] benchmarks have high level of regressions.
ursa-i9-9960x