x/telemetry/config: add telemetry for add and remove struct tags refactoring operations

[madelinekalil]

Summary

As part of the efforts to reduce third party dependencies in the VSCode go extension, we added refactoring codeactions for add and remove struct tags in gopls. Before we can remove the extension functionality for struct tags, we need to evaluate whether people are using the gopls replacement.

We will add two new counters:
gopls/structtags:add - user initiates add struct tags refactoring codeaction
gopls/structtags:remove - user initiates add remove tags refactoring codeaction

Proposed Config Change

https://go-review.git.corp.google.com/c/telemetry/+/688175