feat: Custom message files (#1992)

* feat: add get custom message text to admin api

* feat: read custom message texts from files

* feat: get languages in apis

* feat: get languages in apis

* feat: get languages in apis

* feat: pr feedback

* feat: docs

* feat: merge main

internal/domain/custom_message_text.go

@@ -0,0 +1,66 @@
+package domain
+
+import (
+	"golang.org/x/text/language"
+
+	"github.com/caos/zitadel/internal/eventstore/v1/models"
+)
+
+const (
+	InitCodeMessageType      = "InitCode"
+	PasswordResetMessageType = "PasswordReset"
+	VerifyEmailMessageType   = "VerifyEmail"
+	VerifyPhoneMessageType   = "VerifyPhone"
+	DomainClaimedMessageType = "DomainClaimed"
+	MessageTitle             = "Title"
+	MessagePreHeader         = "PreHeader"
+	MessageSubject           = "Subject"
+	MessageGreeting          = "Greeting"
+	MessageText              = "Text"
+	MessageButtonText        = "ButtonText"
+	MessageFooterText        = "Footer"
+)
+
+type MessageTexts struct {
+	InitCode      CustomMessageText
+	PasswordReset CustomMessageText
+	VerifyEmail   CustomMessageText
+	VerifyPhone   CustomMessageText
+	DomainClaimed CustomMessageText
+}
+
+type CustomMessageText struct {
+	models.ObjectRoot
+
+	State           PolicyState
+	Default         bool
+	MessageTextType string
+	Language        language.Tag
+	Title           string
+	PreHeader       string
+	Subject         string
+	Greeting        string
+	Text            string
+	ButtonText      string
+	FooterText      string
+}
+
+func (m *CustomMessageText) IsValid() bool {
+	return m.MessageTextType != "" && m.Language != language.Und
+}
+
+func (m *MessageTexts) GetMessageTextByType(msgType string) *CustomMessageText {
+	switch msgType {
+	case InitCodeMessageType:
+		return &m.InitCode
+	case PasswordResetMessageType:
+		return &m.PasswordReset
+	case VerifyEmailMessageType:
+		return &m.VerifyEmail
+	case VerifyPhoneMessageType:
+		return &m.VerifyPhone
+	case DomainClaimedMessageType:
+		return &m.DomainClaimed
+	}
+	return nil
+}