Adds freeze option in NavigationSE2Action, improves observation MDPs

[pascal-roth]

Description

Added

• Added freeze_low_level_policy option to :NavigationSE2ActionCfg to allow to not freeze the low level policy.
• Added nan_fill_value option to camera_image to allow to fill NaNs with a specific value.

Changed

• Updated height_scan_clipped to make clipping optional.

Type of change

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

Checklist

• I have run the pre-commit checks with ./formatter.sh
• I have made corresponding changes to the documentation (will come shortly)
• My changes generate no new warnings
• 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