Refactor Vector to make more sense in naming 'field'

[prmukherj]

Currently 'Vector' takes in an argument 'field' which actually should be 'color_by' as it is a scalar field using which the velocity vectors are colored. Moreover, currently visualization supports only velocity vector which should be properly covered in documentation as well. The field currently takes a scalar field but plots vector which might be confusing for users.

[prmukherj]

velocity_vector_object = Vector(
solver=solver_session,
field="velocity",
color_by="x-velocity",
surfaces=["solid_up:1:830"],
scale=2,
)