Update CDF-TTFB graph
We're planning to add the CDF-TTFB graph discussed in legacy/trac#33076 (moved) to OnionPerf, but it looks like OnionPerf already contains a very similar graph. We'll know for sure after resolving legacy/trac#33255 (moved). We'll probably want to make changes to that graph to be more similar what we discussed in legacy/trac#33076 (moved). For example, we'll want to split observations based on start time to distinguish experiment time from the time before and after, and we'll want to add subplots for different facets of the data like source or public/onion server.