MM-24530-Add support for search terms with underscore using postgresql engine (#16618)

* add support for search terms with underscore using postgresql

* fix failing tests

Initially issue fix applied to all search terms instead of the ones that contains _

* direct cast tsquery

* fix test issues

* refactor underscored quoted term search

* support search term case-insensitive

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

store/sqlstore/post_store.go

@@ -1481,7 +1481,16 @@ func (s *SqlPostStore) search(teamId string, userId string, params *model.Search
 			queryParams["Terms"] = "(" + strings.Join(strings.Fields(terms), " & ") + ")" + excludeClause
 		}
 
-		searchClause := fmt.Sprintf("AND to_tsvector('english', %s) @@  to_tsquery('english', :Terms)", searchType)
+		searchClause := ""
+		if strings.Contains(terms, "_") {
+			//Strip quotes off terms with it
+			if strings.Contains(terms, "\"") {
+				queryParams["Terms"] = strings.ReplaceAll(queryParams["Terms"].(string), "\"", "")
+			}
+			searchClause = fmt.Sprintf("AND lower(%s)::tsvector @@ lower(:Terms)::tsquery", searchType)
+		} else {
+			searchClause = fmt.Sprintf("AND to_tsvector('english', %s) @@  to_tsquery('english', :Terms)", searchType)
+		}
 		searchQuery = strings.Replace(searchQuery, "SEARCH_CLAUSE", searchClause, 1)
 	} else if s.DriverName() == model.DATABASE_DRIVER_MYSQL {
 		if searchType == "Message" {