Add Optifine To 1.21

[toxic vine]

is good for playing with shaders and better performance than iris mod.

[cinder bear]

1. Optifine isn't even out for 1.21 yet.
2. Iris has nothing to do with optimization, it handles shaders. Sodium does the optimization stuff.
3. Your average FPS and general performance with Sodium will always exceed Optifine's.

[unique cypress]

+1

[signal creek]

+1

Perfectly worded