The TextureMipmapLimitGroup to use the mipmap limit of.
The texture uses the mipmap limit of groupName if you set MipmapLimitDescriptor.useMipmapLimit to true.
If no group is provided (either String.Empty() or null), the texture will use the global mipmap limit.
If a group is provided but it has not been defined in the Unity Project (set up in the Project's Quality Settings, or managed via TextureMipmapLimitGroups), the texture also falls back to following the global mipmap limit.