Allow admin to associate missing LFS objects for repositories (#18143)

This PR reworked the Find pointer files feature in Settings -> LFS page.

When a LFS object is missing from database but exists in LFS content store, admin can associate it to the repository by clicking the Associate button.

This PR is not perfect (because the LFS module itself should be improved too), it's just a nice-to-have feature to help users recover their LFS repositories (eg: database was lost / table was truncated)

templates/repo/settings/lfs_pointers.tmpl

@@ -11,7 +11,7 @@
 					<form class="ui form" method="post" action="{{$.Link}}/associate">
 						{{.CsrfTokenHtml}}
 						{{range .Pointers}}
-							{{if and (not .InRepo) .Exists .Accessible}}
+							{{if .Associatable}}
 								<input type="hidden" name="oid" value="{{.Oid}} {{.Size}}"/>
 							{{end}}
 						{{end}}