Add Cargo package registry (#21888)

This PR implements a [Cargo registry](https://doc.rust-lang.org/cargo/)
to manage Rust packages. This package type was a little bit more
complicated because Cargo needs an additional Git repository to store
its package index.

Screenshots:

![grafik](https://user-images.githubusercontent.com/1666336/203102004-08d812ac-c066-4969-9bda-2fed818554eb.png)

![grafik](https://user-images.githubusercontent.com/1666336/203102141-d9970f14-dca6-4174-b17a-50ba1bd79087.png)

![grafik](https://user-images.githubusercontent.com/1666336/203102244-dc05743b-78b6-4d97-998e-ef76341a978f.png)

---------

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

routers/web/user/setting/packages.go

@@ -77,3 +77,21 @@ func PackagesRulePreview(ctx *context.Context) {
 
 	ctx.HTML(http.StatusOK, tplSettingsPackagesRulePreview)
 }
+
+func InitializeCargoIndex(ctx *context.Context) {
+	ctx.Data["Title"] = ctx.Tr("packages.title")
+	ctx.Data["PageIsSettingsPackages"] = true
+
+	shared.InitializeCargoIndex(ctx, ctx.Doer)
+
+	ctx.Redirect(setting.AppSubURL + "/user/settings/packages")
+}
+
+func RebuildCargoIndex(ctx *context.Context) {
+	ctx.Data["Title"] = ctx.Tr("packages.title")
+	ctx.Data["PageIsSettingsPackages"] = true
+
+	shared.RebuildCargoIndex(ctx, ctx.Doer)
+
+	ctx.Redirect(setting.AppSubURL + "/user/settings/packages")
+}