Added tests for combined rate-limiting bucket, including # trials and response status codes for each trial

Added tagged test (rate-limit-combined) for testing rate-limiting function using a new variable, "fraction", which is then * by rate_limit numerator in .env file and then += 1 to ensure that the combined total of all rate_limiting trials (create issue + create notes) during the test will exceed allowed rate and raise 403 exception.

All tests passing at 94 percent coverage per python coverage.