Awarding passive income

[bzns]

• During the game, at the end of each preparation phase, the active players will receive interest based on their wealth.
• At the end of each preparation phase, the player profiles will be updated with the new amount of gold
• The updated value will be returned to the client during its next /games/{gameId} GET request

Estimated time: 4h
This task is part of user story #22

[Thahit]

it is debatable when to give the interest, and weather to return the gold count, but interest exists
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