Rename VectorNeumannBC as it does not work for vector variables

[GiudGiud]

Reason

Two users got caught. I had to check the code to realize what it does.
Of course if everyone (including me) read the documentation carefully we would not get caught

Design

Change the name
Maybe DirectionalNeumannBC ?

Impact

Lost user time, user support expenditure

Discussed in #27105

^{Originally posted by TLWise March 15, 2024}
I am attempting to use the VectorNeumannBC with the vector velocity. I get the following error:
No standard variable named velocity found. Did you specify a vector variable when you meant to specify a standard variable?

Is it possible to use VectorNeumannBC with the NS variable velocity?