✨ Added Motor Group Append/Erase Functions

[Gracelu128]

Summary:

Added append function that takes in port number and erase function that takes in reference to motor group.

Motivation:

The append function previously required a reference to the motor group, and the erase function required a port number. This update allows the append function to accept a port number, and the erase function to use a reference to the motor group.

Test Plan:

• Try appending port via port number to motor group
• Try erasing motors in motor group via reference to motor group