333 modify mobile base for consistency

[glannuzel]

Mobile base API is now the same as for other parts.

To use with:

• reachy2-sdk-api : https://github.com/pollen-robotics/reachy2-sdk-api/pull/120
• reachy2_sdk_server : https://github.com/pollen-robotics/reachy2_sdk_server/pull/158