Filter stop words when searching posts in mysql (#14509)

store/searchlayer/stop_word.go

@@ -0,0 +1,7 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package searchlayer
+
+var MYSQL_STOP_WORDS = []string{"a", "about", "an", "are", "as", "at", "be", "by", "com", "de", "en", "for", "from", "how", "i", "in", "is", "it", "la", "of",
+	"on", "or", "that", "the", "this", "to", "was", "what", "when", "where", "who", "will", "with", "und", "the", "www"}