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)

routers/web/repo/lfs.go

@@ -421,12 +421,13 @@ func LFSPointerFiles(ctx *context.Context) {
 		var numAssociated, numNoExist, numAssociatable int
 
 		type pointerResult struct {
-			SHA        string
-			Oid        string
-			Size       int64
-			InRepo     bool
-			Exists     bool
-			Accessible bool
+			SHA          string
+			Oid          string
+			Size         int64
+			InRepo       bool
+			Exists       bool
+			Accessible   bool
+			Associatable bool
 		}
 
 		results := []pointerResult{}
@@ -461,22 +462,29 @@ func LFSPointerFiles(ctx *context.Context) {
 					// Can we fix?
 					// OK well that's "simple"
 					// - we need to check whether current user has access to a repo that has access to the file
-					result.Accessible, err = models.LFSObjectAccessible(ctx.User, pointerBlob.Oid)
+					result.Associatable, err = models.LFSObjectAccessible(ctx.User, pointerBlob.Oid)
 					if err != nil {
 						return err
 					}
-				} else {
-					result.Accessible = true
+					if !result.Associatable {
+						associated, err := models.LFSObjectIsAssociated(pointerBlob.Oid)
+						if err != nil {
+							return err
+						}
+						result.Associatable = !associated
+					}
 				}
 			}
 
+			result.Accessible = result.InRepo || result.Associatable
+
 			if result.InRepo {
 				numAssociated++
 			}
 			if !result.Exists {
 				numNoExist++
 			}
-			if !result.InRepo && result.Accessible {
+			if result.Associatable {
 				numAssociatable++
 			}