documentation update

[padhupradheep]

• link autonomous navigation to the getting started page
• talk about the available default maps for simulation

[AdarshKaran]

• We also need to update the ros2 gripper action command in docs since we have migrated to ParallelActionGrippers (Added back gripper and updated to parallel_gripper_action_controller #102)

[padhupradheep]

Add information about how to change the teleop speed

[padhupradheep]

Route server documentation needs to be updated

@AdarshKaran