MM-14620 Specify parameter name for PluginAPI.GetUsers (#10456)

This is to fix the generated code so that it actually passes arguments correctly. If you look at the diff, the client-side call doesn't actually pass any values for the unnamed parameter.

I also filed https://mattermost.atlassian.net/browse/MM-14621 in case we want to actually fix the generator code.

#### Ticket Link
https://mattermost.atlassian.net/browse/MM-14620

plugin/api.go

@@ -74,7 +74,7 @@ type API interface {
 	// GetUsers a list of users based on search options.
 	//
 	// Minimum server version: 5.10
-	GetUsers(*model.UserGetOptions) ([]*model.User, *model.AppError)
+	GetUsers(options *model.UserGetOptions) ([]*model.User, *model.AppError)
 
 	// GetUser gets a user.
 	GetUser(userId string) (*model.User, *model.AppError)