MM - 19155 Change plugin helpers files to be golint complied (#12686)

* MM-19155 Change plugin helpers files to be golint complied

* add makefile target that checks if plugin/helpers files are golint
  compliant

* MM-19155 - Change plugin helpers files to be golint complied

* added comment documentation to exported plugin/helpers methods
* changed variable names to be compliant with golint

* Address feedback

plugin/helpers.go

@@ -9,6 +9,9 @@ import (
 	"github.com/pkg/errors"
 )
 
+// Helpers provide a common patterns plugins use.
+//
+// Plugins obtain access to the Helpers by embedding MattermostPlugin.
 type Helpers interface {
 	// EnsureBot either returns an existing bot user matching the given bot, or creates a bot user from the given bot.
 	// Returns the id of the resulting bot.
@@ -55,6 +58,7 @@ type Helpers interface {
 	KVSetWithExpiryJSON(key string, value interface{}, expireInSeconds int64) error
 }
 
+// HelpersImpl implements the helpers interface with an API that retrieves data on behalf of the plugin.
 type HelpersImpl struct {
 	API API
 }