Endpoint metrics are not format specific

Some of the endpoints where we'd been working lately don't reflect properly performance issues, method timings, method calls count. For some endpoints, the same controller action does a lot of different things based on the requests format. The most relevant case I think it's the MergeRequests controller where #show, #builds, #pipelines, #commits, #diffs all those action requested as HTML format should perform almost in the same way but differently when requested for example as json.

• Could we split the metrics by request format?