Read version for docker image from text file

[pmolodo]

Description

The latest version of rl-baselines3-zoo is 2.3.0, but the tag on docker is still 2.2.0a1 - this updates build_docker.sh so it tags it correctly.

Motivation and Context

• I have raised an issue to propose this change (required for new features and bug fixes) - [Bug]: Docker tag is still 2.2.0a2, but latest rl-baselines3-zoo is now 2.3.0 #455

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)

Checklist:

• I've read the CONTRIBUTION guide (required)
• I have updated the changelog accordingly (required).
  I didn't think the CHANGLOG needed to be updated for this - ie, if I put it in the 2.3.0 section, the note would be something like, "made docker tag 2.3.0", which seems unnecessary
• My change requires a change to the documentation.
• I have updated the tests accordingly (required for a bug fix or a new feature).
• I have updated the documentation accordingly.
• I have reformatted the code using make format (required)
• I have checked the codestyle using make check-codestyle and make lint (required)
• I have ensured make pytest and make type both pass. (required)

Note: we are using a maximum length of 127 characters per line

[araffin]

The latest version of rl-baselines3-zoo is 2.3.0, but the tag on docker is still 2.2.0a1 - this updates build_docker.sh so it tags it correctly.

Actually this version is for the base image, which defined in https://github.com/DLR-RM/stable-baselines3/blob/master/scripts/build_docker.sh

The latest version for SB3 docker image is 2.2.0a1: https://hub.docker.com/r/stablebaselines/stable-baselines3/tags