Update manifest with h5n1-cattle-outbreak segments

See <nextstrain/avian-flu#69> and
<nextstrain/avian-flu#72> for details of the new
datasets themselves.

Segments ordered following the other avian-flu builds in the manifest,
although note that this order differs from the canonical order of
"pb2", "pb1", "pa", "ha","np", "na", "mp", "ns" which is used to order
segments in the avian-flu/h5n1-cattle-outbreak/genome build.

data/manifest_core.json

@@ -6,6 +6,14 @@
           "h5n1-cattle-outbreak": {
               "segment": {
                   "genome": "",
+                  "ha": "",
+                  "mp": "",
+                  "na": "",
+                  "ns": "",
+                  "np": "",
+                  "ps": "",
+                  "pb1": "",
+                  "pb2": "",
                   "default": "genome"
               }
           },