Fixes Franka blueprint env ID in docs

[louislelay]

Description

Replace the incorrect env ID Isaac-Stack-Cube-Franka-Blueprint-v0 with the correct Isaac-Stack-Cube-Franka-IK-Rel-Blueprint-v0 on the environments list page to match what’s registered in code and shown by scripts/environments/list_envs.py.

Fixes #3207

Type of change

• Bug fix (non-breaking change which fixes an issue)
• This change requires a documentation update

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

[ooctipus]

@louislelay

Thank you Louis!!!! (๑˃ᴗ˂)ﻭ

[ooctipus]

Good Job! All tests passed!

[louislelay]

No worries @ooctipus, thanks for taking the time to look at it! 😁