format headers in python and other small tweaks

[dkuku]

Description

@j-bennet I moved the tuple key but it does not change anything. This is unused. I can't find this in the code so no way to write a test for that. I tried to extend the tests but it breaks other tests so it's a bit complicated. In this pr I also added a docker file and a script to run the tests against multiple versions of postgres using a single command And I made a simple formatter for the headers - this way in the quotes in the queries are redundant.

Checklist

nothing really to add to the changelog.

• [x] I've added this contribution to the changelog.rst.
• [x] I installed pre-commit hooks (pip install pre-commit && pre-commit install), and ran black on my code.
• [x] Please squash merge this pull request (uncheck if you'd like us to merge as multiple commits)

[dkuku]

I also compared the output from current pgcli against psql on few production tables: I see we are not showing:

• Publications
• Statistics objects
• Access method

[j-bennet]

Thanks @dkuku , this looks nice.