MM-21626, MM-21627 - Plugin API/Hooks Prometheus instrumentati… (#13825)

* MM-21626,MM-21627 - Plugin API/Hooks Prometheus instrumentation

* Updated einterface mocks

* Fixed supervisor tests

* ignoring golint errors for plugin metrics wrappers

* Making golangci happy

* Using variadic form when generating wrapper code

* Removed artificial delay

* Removed comments from tests

* Renaming plugin wrappers to api/hooks_timer_layer

* updating vendor dir and mod files

* Recording plugin api/hook responses in prometheus

* Updated einterfaces-mocks

* Updating go sum

* Updating go sum

* Fixing conflicts

* More conflicts fixing

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

go.mod

@@ -66,6 +66,7 @@ require (
 	github.com/pelletier/go-toml v1.6.0 // indirect
 	github.com/pkg/errors v0.9.1
 	github.com/prometheus/client_golang v1.4.0
+	github.com/prometheus/client_model v0.2.0
 	github.com/reflog/struct2interface v0.3.0 // indirect
 	github.com/rs/cors v1.7.0
 	github.com/russellhaering/goxmldsig v0.0.0-20180430223755-7acd5e4a6ef7