Refactor and enhance issue indexer to support both searching, filtering and paging (#26012)

Fix #24662.

Replace #24822 and #25708 (although it has been merged)


## Background

In the past, Gitea supported issue searching with a keyword and
conditions in a less efficient way. It worked by searching for issues
with the keyword and obtaining limited IDs (as it is heavy to get all)
on the indexer (bleve/elasticsearch/meilisearch), and then querying with
conditions on the database to find a subset of the found IDs. This is
why the results could be incomplete.

To solve this issue, we need to store all fields that could be used as
conditions in the indexer and support both keyword and additional
conditions when searching with the indexer.

## Major changes

- Redefine `IndexerData` to include all fields that could be used as
filter conditions.
- Refactor `Search(ctx context.Context, kw string, repoIDs []int64,
limit, start int, state string)` to `Search(ctx context.Context, options
*SearchOptions)`, so it supports more conditions now.
- Change the data type stored in `issueIndexerQueue`. Use
`IndexerMetadata` instead of `IndexerData` in case the data has been
updated while it is in the queue. This also reduces the storage size of
the queue.
- Enhance searching with Bleve/Elasticsearch/Meilisearch, make them
fully support `SearchOptions`. Also, update the data versions.
- Keep most logic of database indexer, but remove
`issues.SearchIssueIDsByKeyword` in `models` to avoid confusion where is
the entry point to search issues.
- Start a Meilisearch instance to test it in unit tests.
- Add unit tests with almost full coverage to test
Bleve/Elasticsearch/Meilisearch indexer.

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

models/issues/label.go

@@ -272,12 +272,12 @@ func GetLabelByID(ctx context.Context, labelID int64) (*Label, error) {
 }
 
 // GetLabelsByIDs returns a list of labels by IDs
-func GetLabelsByIDs(labelIDs []int64) ([]*Label, error) {
+func GetLabelsByIDs(labelIDs []int64, cols ...string) ([]*Label, error) {
 	labels := make([]*Label, 0, len(labelIDs))
 	return labels, db.GetEngine(db.DefaultContext).Table("label").
 		In("id", labelIDs).
 		Asc("name").
-		Cols("id", "repo_id", "org_id").
+		Cols(cols...).
 		Find(&labels)
 }
 
@@ -476,6 +476,18 @@ func GetLabelsByOrgID(ctx context.Context, orgID int64, sortType string, listOpt
 	return labels, sess.Find(&labels)
 }
 
+// GetLabelIDsByNames returns a list of labelIDs by names.
+// It doesn't filter them by repo or org, so it could return labels belonging to different repos/orgs.
+// It's used for filtering issues via indexer, otherwise it would be useless.
+// Since it could return labels with the same name, so the length of returned ids could be more than the length of names.
+func GetLabelIDsByNames(ctx context.Context, labelNames []string) ([]int64, error) {
+	labelIDs := make([]int64, 0, len(labelNames))
+	return labelIDs, db.GetEngine(ctx).Table("label").
+		In("name", labelNames).
+		Cols("id").
+		Find(&labelIDs)
+}
+
 // CountLabelsByOrgID count all labels that belong to given organization by ID.
 func CountLabelsByOrgID(orgID int64) (int64, error) {
 	return db.GetEngine(db.DefaultContext).Where("org_id = ?", orgID).Count(&Label{})