More notification metrics fixes (#26889)

* Explicitly have the client tell the server when it should expect an ACK

* Don't count missing profile errors for your own posts, added comment

* Fix test

* Make postedAck a parameter in WebSocketClient

* Snapshot fixes

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/api4/websocket.go

@@ -17,6 +17,7 @@ import (
 const (
 	connectionIDParam   = "connection_id"
 	sequenceNumberParam = "sequence_number"
+	postedAckParam      = "posted_ack"
 )
 
 func (api *API) InitWebSocket() {
@@ -48,6 +49,7 @@ func connectWebSocket(c *Context, w http.ResponseWriter, r *http.Request) {
 		TFunc:     c.AppContext.T,
 		Locale:    "",
 		Active:    true,
+		PostedAck: r.URL.Query().Get(postedAckParam) == "true",
 	}
 	// The WebSocket upgrade request coming from mobile is missing the
 	// user agent so we need to fallback on the session's metadata.