Add text support on Ogre2

[chapulina]

Desired behavior

I'd like to write text to the 3D scene with Ogre 2 like we have with Ogre 1. See this tutorial, which only applies to Ogre 1:

https://ignitionrobotics.org/api/rendering/7.0/text_geom.html

Alternatives considered

N/A

Implementation suggestion

This function needs to be filled:

https://github.com/ignitionrobotics/ign-rendering/blob/056023a9f8f139925035b0e62db3837ad9a3f8e3/ogre2/src/Ogre2Scene.cc#L1190-L1195

We need to create a Ogre2Text class like we have an OgreText.

Additional context

I'm not sure what's the current status of MovableText support in Ogre 2, this thread has more context: https://forums.ogre3d.org/viewtopic.php?t=82872