feat: added xoauth for smtp (#11239)

# Which Problems Are Solved

- Some mail providers (e.g.: MS Exchange) have deprecated plain auth

# How the Problems Are Solved

Adds XOauth2 auth option to SMPT
- SMTP config now can contain XOAuth2 auth config
- Proto files are updated to have a oneof for configuration selection.
Old fields for configuring plain auth are still available not to create
a breaking change. These can be removed in the future.
- Columns are added to the database to persist the config

# Additional Changes

none

# Additional Context

Replace this example with links to related issues, discussions, discord
threads, or other sources with more context.
Use the Closing #issue syntax for issues that are resolved with this PR.
- Closes #8042

---------

Co-authored-by: Copilot <[email protected]>
Co-authored-by: Tim Möhlmann <[email protected]>

internal/command/instance.go

@@ -520,6 +520,14 @@ func setupSMTPSettings(commands *Commands, validations *[]preparation.Validation
 	if smtpConfig == nil {
 		return
 	}
+	var username string
+	var pwd []byte
+	if smtpConfig.SMTP.PlainAuth != nil {
+		username = smtpConfig.SMTP.PlainAuth.User
+		if smtpConfig.SMTP.PlainAuth != nil {
+			pwd = []byte(smtpConfig.SMTP.PlainAuth.Password)
+		}
+	}
 	*validations = append(*validations,
 		commands.prepareAddAndActivateSMTPConfig(
 			instanceAgg,
@@ -528,8 +536,8 @@ func setupSMTPSettings(commands *Commands, validations *[]preparation.Validation
 			smtpConfig.FromName,
 			smtpConfig.ReplyToAddress,
 			smtpConfig.SMTP.Host,
-			smtpConfig.SMTP.User,
-			[]byte(smtpConfig.SMTP.Password),
+			username,
+			pwd,
 			smtpConfig.Tls,
 		),
 	)