Make issue and code search support camel case (#22829)

Fixes #22714 
### Changes:
1. Add a token filter which named "camelCase" between custom unicode
token filter and "to_lower" token filter when add custom analyzer.

### Notice:
If users want this feature to work, they should delete folder under
{giteaPath}/data/indexers and restart application. Then application will
create a new IndexMapping.

### Screenshots:

![image](https://user-images.githubusercontent.com/33891828/217715692-c18c41f2-57a1-4727-861c-470935c8e0c8.png)

### Others:
I originally attempted to give users the ability to configure the
"token_filters" in the "app.ini" file. But I found that if users does
not strictly follow a right order to register "token_filters", they
won't get the expected results. I think it is difficult to ask users to
do this. So I finally give up this idea.

---------

Co-authored-by: Jason Song <i@wolfogre.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/indexer/code/bleve.go

@@ -27,6 +27,7 @@ import (
 	"github.com/blevesearch/bleve/v2"
 	analyzer_custom "github.com/blevesearch/bleve/v2/analysis/analyzer/custom"
 	analyzer_keyword "github.com/blevesearch/bleve/v2/analysis/analyzer/keyword"
+	"github.com/blevesearch/bleve/v2/analysis/token/camelcase"
 	"github.com/blevesearch/bleve/v2/analysis/token/lowercase"
 	"github.com/blevesearch/bleve/v2/analysis/token/unicodenorm"
 	"github.com/blevesearch/bleve/v2/analysis/tokenizer/unicode"
@@ -107,7 +108,7 @@ func (d *RepoIndexerData) Type() string {
 const (
 	repoIndexerAnalyzer      = "repoIndexerAnalyzer"
 	repoIndexerDocType       = "repoIndexerDocType"
-	repoIndexerLatestVersion = 5
+	repoIndexerLatestVersion = 6
 )
 
 // createBleveIndexer create a bleve repo indexer if one does not already exist
@@ -138,7 +139,7 @@ func createBleveIndexer(path string, latestVersion int) (bleve.Index, error) {
 		"type":          analyzer_custom.Name,
 		"char_filters":  []string{},
 		"tokenizer":     unicode.Name,
-		"token_filters": []string{unicodeNormalizeName, lowercase.Name},
+		"token_filters": []string{unicodeNormalizeName, camelcase.Name, lowercase.Name},
 	}); err != nil {
 		return nil, err
 	}

modules/indexer/issues/bleve.go

@@ -15,6 +15,7 @@ import (
 
 	"github.com/blevesearch/bleve/v2"
 	"github.com/blevesearch/bleve/v2/analysis/analyzer/custom"
+	"github.com/blevesearch/bleve/v2/analysis/token/camelcase"
 	"github.com/blevesearch/bleve/v2/analysis/token/lowercase"
 	"github.com/blevesearch/bleve/v2/analysis/token/unicodenorm"
 	"github.com/blevesearch/bleve/v2/analysis/tokenizer/unicode"
@@ -27,7 +28,7 @@ import (
 const (
 	issueIndexerAnalyzer      = "issueIndexer"
 	issueIndexerDocType       = "issueIndexerDocType"
-	issueIndexerLatestVersion = 1
+	issueIndexerLatestVersion = 2
 )
 
 // indexerID a bleve-compatible unique identifier for an integer id
@@ -134,7 +135,7 @@ func createIssueIndexer(path string, latestVersion int) (bleve.Index, error) {
 		"type":          custom.Name,
 		"char_filters":  []string{},
 		"tokenizer":     unicode.Name,
-		"token_filters": []string{unicodeNormalizeName, lowercase.Name},
+		"token_filters": []string{unicodeNormalizeName, camelcase.Name, lowercase.Name},
 	}); err != nil {
 		return nil, err
 	}