Add inbucket docker image to allow local and automated testing of emails (#4901)

* add docker container for inbucket

* Add way to get the emails using inbucket and add a test for reset password

* add config setting to send emails

* update TestEmailTest

update

* add another test and fix wrong assert

* update per review

fix lint

change senders email

* Revert config.json to default values for EmailSettings section

* update test

* add setup to make the test run

app/apptestlib.go

@@ -53,6 +53,7 @@ func Setup() *TestHelper {
 		NewServer()
 		InitStores()
 		StartServer()
+		utils.InitHTML()
 		utils.EnableDebugLogForTest()
 		Srv.Store.MarkSystemRanUnitTests()
 

app/notification_test.go

@@ -178,6 +178,7 @@ func TestGetExplicitMentionsAtHere(t *testing.T) {
 }
 
 func TestGetMentionKeywords(t *testing.T) {
+	Setup()
 	// user with username or custom mentions enabled
 	user1 := &model.User{
 		Id:        model.NewId(),