Adds option to define the concatenation dimension in the ObservationManager and change counter update in CommandManager

[pascal-roth]

Description

Added support for concatenation of observations along different dimensions in ObservationManager.

Updates the position where the command counter is increased to allow checking for reset environments in the resample call of the CommandManager

Type of change

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

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

[jtigue-bdai]

@pascal-roth what do you think of this compared to (or in addition to): #1958