Extracting email functions into a service (#14802)

* Extracting email functions into a service

* Fixing two shadowing errors

* Address PR review comments

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

app/app_iface.go

@@ -334,7 +334,6 @@ type AppIface interface {
 	AddChannelMember(userId string, channel *model.Channel, userRequestorId string, postRootId string) (*model.ChannelMember, *model.AppError)
 	AddConfigListener(listener func(*model.Config, *model.Config)) string
 	AddDirectChannels(teamId string, user *model.User) *model.AppError
-	AddNotificationEmailToBatch(user *model.User, post *model.Post, team *model.Team) *model.AppError
 	AddSamlIdpCertificate(fileData *multipart.FileHeader) *model.AppError
 	AddSamlPrivateCertificate(fileData *multipart.FileHeader) *model.AppError
 	AddSamlPublicCertificate(fileData *multipart.FileHeader) *model.AppError
@@ -424,7 +423,6 @@ type AppIface interface {
 	CreateUserFromSignup(user *model.User) (*model.User, *model.AppError)
 	CreateUserWithInviteId(user *model.User, inviteId string) (*model.User, *model.AppError)
 	CreateUserWithToken(user *model.User, token *model.Token) (*model.User, *model.AppError)
-	CreateVerifyEmailToken(userId string, newEmail string) (*model.Token, *model.AppError)
 	CreateWebhookPost(userId string, channel *model.Channel, text, overrideUsername, overrideIconUrl, overrideIconEmoji string, props model.StringInterface, postType string, postRootId string) (*model.Post, *model.AppError)
 	DataRetention() einterfaces.DataRetentionInterface
 	DeactivateGuests() *model.AppError
@@ -852,15 +850,10 @@ type AppIface interface {
 	SendAckToPushProxy(ack *model.PushNotificationAck) error
 	SendAutoResponse(channel *model.Channel, receiver *model.User) (bool, *model.AppError)
 	SendAutoResponseIfNecessary(channel *model.Channel, sender *model.User) (bool, *model.AppError)
-	SendDeactivateAccountEmail(email string, locale, siteURL string) *model.AppError
 	SendEmailVerification(user *model.User, newEmail string) *model.AppError
 	SendEphemeralPost(userId string, post *model.Post) *model.Post
-	SendInviteEmails(team *model.Team, senderName string, senderUserId string, invites []string, siteURL string)
 	SendNotifications(post *model.Post, team *model.Team, channel *model.Channel, sender *model.User, parentPostList *model.PostList, setOnline bool) ([]string, error)
 	SendPasswordReset(email string, siteURL string) (bool, *model.AppError)
-	SendPasswordResetEmail(email string, token *model.Token, locale, siteURL string) (bool, *model.AppError)
-	SendRemoveExpiredLicenseEmail(email string, locale, siteURL string, licenseId string) *model.AppError
-	SendSignInChangeEmail(email, method, locale, siteURL string) *model.AppError
 	ServeInterPluginRequest(w http.ResponseWriter, r *http.Request, sourcePluginId, destinationPluginId string)
 	ServePluginRequest(w http.ResponseWriter, r *http.Request)
 	Session() *model.Session