Turn groupColor field value into optional field codec

[jurrejelle]

What

In #4273, the codec for GTRecipe was changed to include a recipeColor field. This field should have been made optional with a default value of -1, for compatability reasons.

How Was This Tested

{"type":"gtceu:alloy_smelter","duration":100,"category":"gtceu:alloy_smelter","tickInputs":{"eu":[{"content":4}]},"inputs":{"item":[{"content":{"type":"gtceu:sized","count":5,"ingredient":{"item":"minecraft:acacia_planks"}}},{"content":{"type":"gtceu:circuit","configuration":15},"chance":0}]},"outputs":{"item":[{"content":{"type":"gtceu:sized","count":1,"ingredient":{"item":"minecraft:acacia_boat"}}}]}}

Additional Information

It is worth noting that support like this for internal structures is an exception, not a rule.