Optional trend lines would be super valuable

[winsmith]

Discussed in https://github.com/TelemetryDeck/Issues/discussions/449

^{Originally posted by mattcorey September 6, 2024} Being able to optionally add trend lines to a graph would be super valuable. I find myself looking at a graph like this, and if I squint a bit, I can figure that I had a slight bump a week or two ago, but it may have settled down:

If I had trend lines, though, it can be much more obvious. For example, a horizontal line showing the weekly averages would actually show that I had a nice 24% bump two weeks ago, followed by a smaller 8% drop, and I could see this information instantly.