[MM-56339] Audit logs: on login add UserId and SessionId to audit's Actor field (#27446)

* on login add UserId and SessionId to audit's Actor field to match logout

* lint

* simplify to add only userId and sessionId

* AddToEventActor -> AddUser/SessionToEventActor

* fill in missing session data when logging the audit record

* why did it bump that? reverting.

* make modules-tidy

* trigger build

* add more context to the comment

server/channels/web/context.go

@@ -29,6 +29,15 @@ type Context struct {
 
 // LogAuditRec logs an audit record using default LevelAPI.
 func (c *Context) LogAuditRec(rec *audit.Record) {
+	// finish populating the context data, in case the session wasn't available during MakeAuditRecord
+	// (e.g., api4/user.go login)
+	if rec.Actor.UserId == "" {
+		rec.Actor.UserId = c.AppContext.Session().UserId
+	}
+	if rec.Actor.SessionId == "" {
+		rec.Actor.SessionId = c.AppContext.Session().Id
+	}
+
 	c.LogAuditRecWithLevel(rec, app.LevelAPI)
 }