Implement permissions specs for mentions. (#2758)

* Implement permissions specs for mentions.
- public boards: admin, editor, commenter can mention team members and auto-add them to board; guests can mention board members
- private boards:  admin, editor, commenter, guest can mention board members
- viewers cannot mention

server/utils/callbackqueue.go

@@ -2,6 +2,7 @@ package utils
 
 import (
 	"context"
+	"runtime/debug"
 	"sync/atomic"
 	"time"
 
@@ -119,7 +120,11 @@ func (cn *CallbackQueue) exec(f CallbackFunc) {
 	// don't let a panic in the callback exit the thread.
 	defer func() {
 		if r := recover(); r != nil {
-			cn.logger.Error("CallbackQueue callback panic", mlog.String("name", cn.name), mlog.Any("panic", r))
+			cn.logger.Error("CallbackQueue callback panic",
+				mlog.String("name", cn.name),
+				mlog.Any("panic", r),
+				mlog.String("stack", string(debug.Stack())),
+			)
 		}
 	}()