x/telemetry/config: add counters for gopls.ui.diagnostic.staticcheck setting

[h9jiang]

Summary

gopls/setting/staticcheck:{true, false} - staticcheck explicitly enabled or disabled

unfortunately we will not be able to capture the unset value but we can do a simple math to figure out the percentage unset. :D

we can use this information to help us figure out whether staticcheck is enabled.

Proposed Config Change

https://go-review.git.corp.google.com/c/telemetry/+/710895

[gopherbot]

Change https://go.dev/cl/710895 mentions this issue: internal/chartconfig: add gopls/setting/staticcheck counter