Adds configurable modifiers to observation manager

[jtigue-bdai]

Description

The goal of this PR is to introduce expanded functionality to observation corruption/realism. This is done by introducing the concept of configurable modifiers. This creates an architecture that can apply a list of custom modifiers to observation data giving flexibility to order of operations. Existing modifiers for clip, scale, bias, and noise can be used. This does so without changing the current functionality. This PR also includes two new modifiers that are stateful (i.e. output is dependent on previous state) that utilize a Callable class. They are a DigitalFilter and an Integrator.

Summary of Additions:

• Adds ModifierCfg and Modifier
• Adds example modifiers functions for bias, scale, clip, noise
• Adds example modifiers classes: DigitalFilter, Integrator
• Adds functionality to ObservationManager to prepare and handle modifiers of observation data
• Adds unit tests for modifiers in test_modifiers.py
• Adds test to test_observation_manager.py to test integration with modifiers

Type of change

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

[jsmith-bdai]

Looks great, thanks for adding test, new docs and a useful feature 🚀