Add upsert support for Postgresql

[kyri-petrou]

Is your idea related to a problem? Please describe.
Being able to upsert to a postgresql table is very often desired for replacing individual records in a table.

Describe the solution you'd like
The same or similar functionality as the one recently added for Mysql would be perfect!

I'm happy to contribute if needed but I might need some help with the testing.

[jaidisido]

This has now been addressed in merged PR #811 and can be tested:

pip uninstall awswrangler -y
pip install git+https://github.com/awslabs/aws-data-wrangler.git@main

until it's available in the next release. Many thanks to @maxispeicher for the work