Automatically update coins prices

[thevahidal]

Now that we have our coin model, it's time to update their prices automatically.

• Find an open/public cryptocurrency API (Coinmarketcap, Coingecko, ...), And write an scheduled task to update coin prices each 30 seconds.
• Create a new endpoint which returns a list of all coins. It should be paginated.
• Create an status endpoint which returns 'healthy' is coin prices are updated in less than a minute ago, or 'unhealthy' otherwise.

[thevahidal]

Well done!

• Secrets should be kept in .env files and ignored by git. e.g. X-CMC_PRO_API_KEY