server: add treemanifestserver bundle2 capability to Mononoke server

Summary: This is required for pushes, without it the pusher assumes we don't need tree manifests

Reviewed By: farnz

Differential Revision: D8139396

fbshipit-source-id: 42ad18b2f437a0b9441c0d84e4519b87f2902c0d

server/src/repo.rs

@@ -260,6 +260,7 @@ fn bundle2caps() -> String {
         ("b2x:infinitepush", vec![]),
         ("b2x:infinitepushscratchbookmarks", vec![]),
         ("pushkey", vec![]),
+        ("treemanifestserver", vec!["True"]),
     ];
 
     let mut encodedcaps = vec![];