[MM-46694] A/B Test: welcome post (#20926)

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

model/feature_flags.go

@@ -72,6 +72,9 @@ type FeatureFlags struct {
 
 	PlanUpgradeButtonText string
 
+	// A/B Test on posting a welcome message
+	SendWelcomePost bool
+
 	PostPriority bool
 }
 
@@ -99,6 +102,7 @@ func (f *FeatureFlags) SetDefaults() {
 	f.CallsEnabled = true
 	f.BoardsProduct = false
 	f.PlanUpgradeButtonText = "upgrade"
+	f.SendWelcomePost = true
 	f.PostPriority = false
 }
 

model/post.go

@@ -44,6 +44,7 @@ const (
 	PostTypeChannelRestored        = "system_channel_restored"
 	PostTypeEphemeral              = "system_ephemeral"
 	PostTypeChangeChannelPrivacy   = "system_change_chan_privacy"
+	PostTypeWelcomePost            = "system_welcome_post"
 	PostTypeAddBotTeamsChannels    = "add_bot_teams_channels"
 	PostTypeSystemWarnMetricStatus = "warn_metric_status"
 	PostTypeMe                     = "me"
@@ -387,6 +388,7 @@ func (o *Post) IsValid(maxPostSize int) *AppError {
 		PostTypeChangeChannelPrivacy,
 		PostTypeAddBotTeamsChannels,
 		PostTypeSystemWarnMetricStatus,
+		PostTypeWelcomePost,
 		PostTypeMe:
 	default:
 		if !strings.HasPrefix(o.Type, PostCustomTypePrefix) {