feat: multiple search indexes (#2514)

* refactor: abstract search interface

* wip: ~

* fix cycle import

* objs update hook

* wip: ~

* Delete search/none

* auto update index while cache changed

* db searcher

TODO: bleve init issue

cannot open index, metadata missing

* fix size type

why float64??

* fix typo

* fix nil pointer using

* api adapt ui

* bleve: fix clear & change struct

internal/search/db/init.go

@@ -0,0 +1,16 @@
+package db
+
+import (
+	"github.com/alist-org/alist/v3/internal/search/searcher"
+)
+
+var config = searcher.Config{
+	Name:       "database",
+	AutoUpdate: true,
+}
+
+func init() {
+	searcher.RegisterSearcher(config, func() (searcher.Searcher, error) {
+		return &DB{}, nil
+	})
+}