Adjust clone timeout error to suggest increasing timeout (#21769)

There are far too many error reports regarding timeouts from migrations.
We should adjust error report to suggest increasing this timeout.

Ref #20680

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/repository/repo.go

@@ -6,6 +6,7 @@ package repository
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -79,6 +80,9 @@ func MigrateRepositoryGitData(ctx context.Context, u *user_model.User,
 		Timeout:       migrateTimeout,
 		SkipTLSVerify: setting.Migrations.SkipTLSVerify,
 	}); err != nil {
+		if errors.Is(err, context.DeadlineExceeded) {
+			return repo, fmt.Errorf("Clone timed out. Consider increasing [git.timeout] MIGRATE in app.ini. Underlying Error: %w", err)
+		}
 		return repo, fmt.Errorf("Clone: %w", err)
 	}