Add more linters to improve code readability (#19989)

Add nakedret, unconvert, wastedassign, stylecheck and nolintlint linters to improve code readability

- nakedret - https://github.com/alexkohler/nakedret - nakedret is a Go static analysis tool to find naked returns in functions greater than a specified function length.
- unconvert - https://github.com/mdempsky/unconvert - Remove unnecessary type conversions
- wastedassign - https://github.com/sanposhiho/wastedassign -  wastedassign finds wasted assignment statements.
- notlintlint -  Reports ill-formed or insufficient nolint directives
- stylecheck - https://staticcheck.io/docs/checks/#ST - keep style consistent
  - excluded: [ST1003 - Poorly chosen identifier](https://staticcheck.io/docs/checks/#ST1003) and [ST1005 - Incorrectly formatted error string](https://staticcheck.io/docs/checks/#ST1005)

modules/indexer/code/elastic_search.go

@@ -348,7 +348,7 @@ func convertResult(searchResult *elastic.SearchResult, kw string, pageSize int)
 		// FIXME: There is no way to get the position the keyword on the content currently on the same request.
 		// So we get it from content, this may made the query slower. See
 		// https://discuss.elastic.co/t/fetching-position-of-keyword-in-matched-document/94291
-		var startIndex, endIndex int = -1, -1
+		var startIndex, endIndex int
 		c, ok := hit.Highlight["content"]
 		if ok && len(c) > 0 {
 			// FIXME: Since the highlighting content will include <em> and </em> for the keywords,