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*

modules/indexer/issues/internal/model.go

@@ -74,6 +74,8 @@ type SearchResult struct {
 type SearchOptions struct {
 	Keyword string // keyword to search
 
+	IsFuzzyKeyword bool // if false the levenshtein distance is 0
+
 	RepoIDs   []int64 // repository IDs which the issues belong to
 	AllPublic bool    // if include all public repositories