Goal ID implementation

Goal IDs exist to dedupe goals when a user creates a new goal. For example, if a user wants to create a HARD CLEAR Mei goal, but one already exists, we should not insert two Goal Documents representing the same thing.

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Hashing

To create the Goal ID, we perform a json stable hash on the game, playtype, charts and criteria of this field.

This enforces that goals are unique on those fields.

The above hash is then returned, prefixed with G.