Use Python3 in Docker image

[nineinchnick]

Description

Python 2 has reached EOL and the launcher works fine with Python 3. I also think Trino used Python 3 before changing the base image, so I'd consider this a bugfix.

Is this change a fix, improvement, new feature, refactoring, or other?
fix

Is this a change to the core query engine, a connector, client library, or the SPI interfaces? (be specific)
docker image

How would you describe this change to a non-technical end user or system administrator?
n/a

Related issues, pull requests, and links

Documentation

(x) No documentation is needed.
( ) Sufficient documentation is included in this PR.
( ) Documentation PR is available with #prnumber.
( ) Documentation issue #issuenumber is filed, and can be handled later.

Release notes

( ) No release notes entries required.
( ) Release notes entries required with the following suggested text:

# Section
* Fix some things. ({issue}`issuenumber`)

[nineinchnick]

I'm not sure if this requires release notes.

[mosabua]

Good call.

[nineinchnick]

Not needed anymore since #13376 got merged