[MM-59363] Shared channel event telemetry (#29024)

* shared channel event tracking

* Update notification.go

Co-authored-by: Miguel de la Cruz <miguel@mcrx.me>

---------

Co-authored-by: Miguel de la Cruz <miguel@mcrx.me>

server/channels/app/post.go

@@ -97,6 +97,21 @@ func (a *App) CreatePostAsUser(c request.CTX, post *model.Post, currentSessionId
 		}
 	}
 
+	if channel.IsShared() {
+		// if not marked as shared we don't try to reach the store, but needs double checking as it might not be truly shared
+		isShared, shErr := a.Srv().Store().SharedChannel().HasChannel(channel.Id)
+		if shErr == nil && isShared {
+			a.Srv().telemetryService.SendTelemetryForFeature(
+				telemetry.TrackSharedChannelsFeature,
+				"shared_channel_posted",
+				map[string]any{
+					telemetry.TrackPropertyUser:    post.UserId,
+					telemetry.TrackPropertyChannel: channel.Id,
+				},
+			)
+		}
+	}
+
 	return rp, nil
 }