Provide user with feedback when yelp api returns error "too many requests"

[thadkingcole]

problem

When multiple users are on the app making searches at the same time, the yelp api seems to not be able to handle all the traffic and returns a "too many requests" error. This is due to a limit on simultaneous API calls, not the daily limit for the yelp API.

When this happens, the covid 19 & results banners get posted to the site, but no data gets displayed.

solutions

• add additional api keys to be used in the case of one returning error 429 "too many requests" (pr additional yelp API key added #48)
• display a modal to the user with information about the site being too busy. Something like the following: "Sorry, the site is experiencing high traffic and can't perform your search at the moment. Please try again later :)"
• slow down how quickly the yelp API calls are made (pr add 1 second delays around multiple yelp API calls to reduce the calls per sec and improve stability #47)