Use a separate admin page to show global stats, remove actions stat (#25062)

Before, Gitea shows the database table stats on the `admin dashboard`
page.

It has some problems:

* `count(*)` is quite heavy. If tables have many records, this blocks
loading the admin page blocks for a long time
* Some users had even reported issues that they can't visit their admin
page because this page causes blocking or `50x error (reverse proxy
timeout)`
* The `actions` stat is not useful. The table is simply too large. Does
it really matter if it contains 1,000,000 rows or 9,999,999 rows?
* The translation `admin.dashboard.statistic_info` is difficult to
maintain.

So, this PR uses a separate page to show the stats and removes the
`actions` stat.


![image](https://github.com/go-gitea/gitea/assets/2114189/babf7c61-b93b-4a62-bfaa-22983636427e)

## ⚠️ BREAKING

The `actions` Prometheus metrics collector has been removed for the
reasons mentioned beforehand.
Please do not rely on its output anymore.

models/db/context.go

@@ -9,7 +9,6 @@ import (
 
 	"xorm.io/builder"
 	"xorm.io/xorm"
-	"xorm.io/xorm/schemas"
 )
 
 // DefaultContext is the default context to run xorm queries in
@@ -241,30 +240,6 @@ func TableName(bean interface{}) string {
 	return x.TableName(bean)
 }
 
-// EstimateCount returns an estimate of total number of rows in table
-func EstimateCount(ctx context.Context, bean interface{}) (int64, error) {
-	e := GetEngine(ctx)
-	e.Context(ctx)
-
-	var rows int64
-	var err error
-	tablename := TableName(bean)
-	switch x.Dialect().URI().DBType {
-	case schemas.MYSQL:
-		_, err = e.Context(ctx).SQL("SELECT table_rows FROM information_schema.tables WHERE tables.table_name = ? AND tables.table_schema = ?;", tablename, x.Dialect().URI().DBName).Get(&rows)
-	case schemas.POSTGRES:
-		// the table can live in multiple schemas of a postgres database
-		// See https://wiki.postgresql.org/wiki/Count_estimate
-		tablename = x.TableName(bean, true)
-		_, err = e.Context(ctx).SQL("SELECT reltuples::bigint AS estimate FROM pg_class WHERE oid = ?::regclass;", tablename).Get(&rows)
-	case schemas.MSSQL:
-		_, err = e.Context(ctx).SQL("sp_spaceused ?;", tablename).Get(&rows)
-	default:
-		return e.Context(ctx).Count(tablename)
-	}
-	return rows, err
-}
-
 // InTransaction returns true if the engine is in a transaction otherwise return false
 func InTransaction(ctx context.Context) bool {
 	_, ok := inTransaction(ctx)