fix: add rpc to metrics-devtools

[achingbrain]

Adds rpc between the metrics impl and the devtools page.

Metrics sends events to devtools, and devtools invokes methods on the metrics.

Change checklist

• [ ] I have performed a self-review of my own code
• [ ] I have made corresponding changes to the documentation if necessary (this includes comments as well)
• [ ] I have added tests that prove my fix is effective or that my feature works