Improved Currency API #3406
Description
Describe the solution you'd like
The Currency API (api/v1/currency/:currencyName and api/v1/currency/:currencyName/top) should allow fetching currency by ID, and should properly return errors when a currency is not found.
Additionally, for top currency holders, since it's an endpoint for a single currency, the currency prop should be changed from the current full currency object to a simple number value.
Additional context
Currently, when a currency is not found, api/v1/currency/:currencyName returns an empty string and api/v1/currency/:currencyName/top returns an HTML error page with code 500