Update BCR maintainers (#420)

Adding user accounts as an escape hatch.

Author: srikrsna-buf

.bcr/metadata.template.json

@@ -5,6 +5,16 @@
       "name": "Protovalidate Team",
       "email": "[email protected]",
       "github": "bcr-buf"
+    },
+    {
+      "name": "Timo Stamm",
+      "email": "[email protected]",
+      "github": "timostamm"
+    },
+    {
+      "name": "Sri Krishna Paritala",
+      "email": "[email protected]",
+      "github": "srikrsna-buf"
     }
   ],
   "repository": ["github:bufbuild/protovalidate"],