added mapping and navigation

I have implemented the mapping and navigation features for bcr_bot using SLAM Toolbox and Nav2. The following mahor changes have been made:

Launch Files:
    Created mapping_launch.py for the mapping process.
    Created navigation_launch.py for the navigation process.
Remapper:
    Added a remapper to remap cmd_vel to bcr_bot/cmd_vel.

These changes enable mapping and navigation using the bcr_bot package itself.

Testing:

I have thoroughly tested the new features, and they are working as expected.

Please review the changes and let me know if any modifications are required.

blackcoffeerobotics / bcr_bot

added mapping and navigation #42