tools/cmd/goimports: add counter for each invocation

[pjweinb]

The tools repository supports two command lines for fixing imports, goimports and gopls imports. They have separate logic and vastly different performance characteristics. It would be useful to understand how often goimports is invoked.

[pjweinb]

Fixed by golang.org#700595

[pjweinb]

https://go-review.git.corp.google.com/c/tools/+/700595
is the CL including the counter

[gopherbot]

Change https://go.dev/cl/701716 mentions this issue: internal/config: add counter for goimports invocation

[findleyr]

Reopening this to track adding the telemetry.