Draft: Add Performance Testing on RequestManager

This is the proposal for adding Performance Testing to our project. The RequestManager was modified to add a performLoadTestWithVirtualUsers() function that allows repeatedly sending requests and retrieving valuable information about the requests: success and failure rates and the average response time. This way we can recreate what popular tools allow us to do: set a fixed amount of requests per virtual user and a number of virtual users that will simultaneously send those requests.

Example of successful integration with the other tests (the Users feature had 16 successful test cases before and 8 bugs identified; now it has 17 successful test cases since a performance test was included).

The performance test included in the Users feature: