Change simple summation to a root sum of squares for vx_error and vy_error in composites

[mliukis]

Consider a change for v3: a code is written as a simple summation of errors. It might be better to add it as a root sum of squares: sqrt(v[xy]_error2 + error2).

https://github.com/nasa-jpl/its_live_production/blob/6ce62c51f956356544c1cc2d46f6e2a8b8a53532/src/itslive_composite.py#L2187-L2192