ochttp: Custom tags

[mlesar]

Currently, I can only use these:

opencensus-go/plugin/ochttp/stats.go

Lines 86 to 115 in 49838f2

	// The following tags are applied to stats recorded by this package. Host, Path
	// and Method are applied to all measures. StatusCode is not applied to
	// ClientRequestCount or ServerRequestCount, since it is recorded before the status is known.
	var (
	// Host is the value of the HTTP Host header.
	//
	// The value of this tag can be controlled by the HTTP client, so you need
	// to watch out for potentially generating high-cardinality labels in your
	// metrics backend if you use this tag in views.
	Host = tag.MustNewKey("http.host")
	// StatusCode is the numeric HTTP response status code,
	// or "error" if a transport error occurred and no status code was read.
	StatusCode = tag.MustNewKey("http.status")
	// Path is the URL path (not including query string) in the request.
	//
	// The value of this tag can be controlled by the HTTP client, so you need
	// to watch out for potentially generating high-cardinality labels in your
	// metrics backend if you use this tag in views.
	Path = tag.MustNewKey("http.path")
	// Method is the HTTP method of the request, capitalized (GET, POST, etc.).
	Method = tag.MustNewKey("http.method")
	// KeyServerRoute is a low cardinality string representing the logical
	// handler of the request. This is usually the pattern registered on the a
	// ServeMux (or similar string).
	KeyServerRoute = tag.MustNewKey("http_server_route")
	)

So, is there a way to add custom ones in some way as SetRoute is doing this?