Update minimum OpenGL version to 4.1
This should be easy as almost all VTK applications out there use 4.5 already. The three OpenGL render window classes will have to drop support for less than 4.1 from and ensure a clean CI.
If not all, most modern computers are capable of 4.5
- Mesa 12 onwards support OpenGL 4.3 (ubuntu 20.04 has mesa 21.2.6, debian 10 has 18.3.6, many distros considered 'old' have a mesa version > 18.)
- macOS only supports upto 4.1, this is the reason we can't aim higher than 4.1