Patch in exact search for meilisearch (#29671)

meilisearch does not have an search option to contorl fuzzynes per query
right now:
 - https://github.com/meilisearch/meilisearch/issues/1192
 - https://github.com/orgs/meilisearch/discussions/377
 - https://github.com/meilisearch/meilisearch/discussions/1096

so we have to create a workaround by post-filter the search result in
gitea until this is addressed.

For future works I added an option in backend only atm, to enable
fuzzynes for issue indexer too.
And also refactored the code so the fuzzy option is equal in logic to
code indexer

---
*Sponsored by Kithara Software GmbH*
Conflicts:
	routers/web/repo/search.go
	trivial context confict s/isMatch/isFuzzy/

modules/indexer/issues/elasticsearch/elasticsearch.go

@@ -19,6 +19,10 @@ import (
 
 const (
 	issueIndexerLatestVersion = 1
+	// multi-match-types, currently only 2 types are used
+	// Reference: https://www.elastic.co/guide/en/elasticsearch/reference/7.0/query-dsl-multi-match-query.html#multi-match-types
+	esMultiMatchTypeBestFields   = "best_fields"
+	esMultiMatchTypePhrasePrefix = "phrase_prefix"
 )
 
 var _ internal.Indexer = &Indexer{}
@@ -141,7 +145,13 @@ func (b *Indexer) Search(ctx context.Context, options *internal.SearchOptions) (
 	query := elastic.NewBoolQuery()
 
 	if options.Keyword != "" {
-		query.Must(elastic.NewMultiMatchQuery(options.Keyword, "title", "content", "comments"))
+
+		searchType := esMultiMatchTypePhrasePrefix
+		if options.IsFuzzyKeyword {
+			searchType = esMultiMatchTypeBestFields
+		}
+
+		query.Must(elastic.NewMultiMatchQuery(options.Keyword, "title", "content", "comments").Type(searchType))
 	}
 
 	if len(options.RepoIDs) > 0 {