Please make `ecosystem_user_id` be 64 hex chars, rather than 32

[rfk]

This field is currently defined as "pattern": "[a-zA-z0-9]{32}". We intend this value to be derived as an FxA scoped key which by default would make it 32 bytes rather than 32 hex chars. If there are no concerns about inflating the size of this identifier, could be please make it be 64 hex chars == 32 bytes in order to simplify handling on the FxA side of things?