Support sb3 wrapper to pre-process env's image obs-space to trigger sb3 natively supported cnn creation pipeline

[ooctipus]

Description

This PR modifies the SB3 Wrapper so that it utilizes the
SB3 natively supported encoder creation on properly defined composite observation space,

SB3's automatic CNN encoding will apply when

1. if observation space of that term is of shape, GrayScale, RGB, or RGBD
2. if agent_cfg has normalized flag, expects data to have channel as the first dimension, and data pre_normalized
3. if agent doesn't has normalized flag, expects data to have space min=0, max=255, dtype=uint8

This PR makes sure the sb3 wrapper adjust environment image term to meet either condition 2 or condition 3 by looking at space's min and max, so sb3 creation pipeline will be applied automatically.

Type of change

• New feature (non-breaking change which adds functionality)

Screenshots

Please attach before and after screenshots of the change if applicable.

Checklist

• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there