mazes/antmaze-v5 documentation change

[LukaszSawala]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes # (issue)

Fixes the 3 issues of the current antmaze-v5 documentation I have noticed while working with it:

• The observation space is 105, not 111, as the 6 contact forces related to the ground link are omitted in v5
• The argument "use_contact_forces" does not exist; the environment has an obs dimensionality of 105 by default
• The reward calculation is different than the one presented: the negative reward is exponentiated before returning.

Type of change

Please delete options that are not relevant.

• Documentation only change (no code changed)

Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have commented my code, particularly in hard-to-understand areas
• 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
• New and existing unit tests pass locally with my changes

(nothing else done as this is just a documentation change)