Change error with `following_error`

[carlossvg]

I propose to change the name of error for the topic state for servos: https://github.com/AcutronicRobotics/HRIM/blob/master/models/actuator/servo/topics/state.xml#L14

Using the name error for the following error could lead to confusions. For example error could be referring also to error codes or fault states. I think it would be more descriptive to use following_error directly.