Update PriceFeedConsumer.sol contract

[andrejrakic]

• Rename the getLatestPrice() function to getChainlinkDataFeedLatestAnswer()
• Revert if returned answer or roundId are zero
• Have a check for a stale answer. The timeStamp/updatedAt should be compared against the storage variable provided by the user that ideally should be a value close to a heartbeat of an actual feed. If block.timestamp - s_usdcUsdFeedHeartbeat is greater than timeStamp contract should revert
• Currently contract returns plain answer. We should format that value based on the decimals() of the feed and token's decimals
• Test all of these edge cases using Chainlink Local
  • https://docs.chain.link/chainlink-local/api-reference/solidity/data-feeds/mockv3aggregator#updateanswer
  • https://docs.chain.link/chainlink-local/api-reference/solidity/data-feeds/mockv3aggregator#updaterounddata
  • https://docs.chain.link/chainlink-local/api-reference/solidity/data-feeds/mockoffchainaggregator#updateminandmaxanswers (optionally)