PLT-7207: Change from fulltext to LIKE search for user filtering (#7343)

* PLT-7202: Switch user search to LIKE queries to avoid fulltext pitfalls.

* Add 2 char name unit test.

* Escape underscores properly.

* Add more tests and fix * handling.

* Make search/indexes case insensitive for postgres.

store/sqlstore/channel_store.go

@@ -1583,7 +1583,7 @@ func (s SqlChannelStore) performSearch(searchQuery string, term string, paramete
 	result := store.StoreResult{}
 
 	// these chars have special meaning and can be treated as spaces
-	for _, c := range specialUserSearchChar {
+	for _, c := range ignoreUserSearchChar {
 		term = strings.Replace(term, c, " ", -1)
 	}