Add metrics auto-instrumentation

[tbrockman]

Use case

While it's possible to distill traces into metrics, it requires some configuration and additional processing which isn't as user-friendly (particularly for people who are inexperienced with observability tooling). It'd also be a bit less intuitive to emit point-in-time metrics as traces (for example, if we start to use the processes API for measuring tab process perf metrics.

We can simplify this by collecting and exporting metrics directly from the extension.

Implementation

• Determine useful metrics we can track given the instrumentation we already have
• Modify the involved OTEL packages to collect and export those metrics