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

server/middlewares/search.go

@@ -0,0 +1,19 @@
+package middlewares
+
+import (
+	"github.com/alist-org/alist/v3/internal/conf"
+	"github.com/alist-org/alist/v3/internal/errs"
+	"github.com/alist-org/alist/v3/internal/setting"
+	"github.com/alist-org/alist/v3/server/common"
+	"github.com/gin-gonic/gin"
+)
+
+func SearchIndex(c *gin.Context) {
+	mode := setting.GetStr(conf.SearchIndex)
+	if mode == "none" {
+		common.ErrorResp(c, errs.SearchNotAvailable, 500)
+		c.Abort()
+	} else {
+		c.Next()
+	}
+}