[MR Analytics] Show percent change since last month

Problem to solve

GitLab, and certainly many other organizations, want to compare Throughput statistics on a month-over-month basis. Specifically, they want to know if Throughput rose or fell versus the prior month. At GitLab we need to calculate percent change in Throughput to build our Throughput Logs, and currently we are investing in custom Sisense dashboards (example - internal) to calculate those numbers.

Proposal

In the Throughput chart, we should add "Change from last month" to the tooltip that appears when hovering over a data point. The values should be measured as percent change since last month. For clarity, positive values should be prefixed by + and negative values by -.

Mockup

This is a very rough mockup, so please ignore anything that looks slightly abnormal: