[feat] add convenience method to create a Position from a LLA

[vishwa2710]

Is your feature request related to a problem? Please describe.
It would be nice to have a convenient static constructor in the Position class to construct it from a LLA.

Describe the solution you'd like

Position Position::fromLLA(const LLA& aLLA, const Shared<Celestial>& aCelestialPtr = nullptr)
{
    Shared<Celestial> centralBody
    if (aCelestialPtr == nullptr) || (!aCelestialPtr.isDefined())
    {
        Shared<Celestial> centralBody = Environment::getGlobalInstance()->accessCentralBody();
    }
...
}

Describe alternatives you've considered
Currently there exists methods in ostk.astrodynamics.utilities to convert position and lla but they are pure python methods.