Add issue template and other fixes

Author: mosuem

.github/ISSUE_TEMPLATE/sse.md

@@ -0,0 +1,5 @@
+---
+name: "package:sse"
+about: "Create a bug or file a feature request against package:sse."
+labels: "package:sse"
+---

pkgs/sse/CONTRIBUTING.md

@@ -4,7 +4,7 @@ description: >-
   Provides client and server functionality for setting up bi-directional
   communication through Server Sent Events (SSE) and corresponding POST
   requests.
-repository: https://github.com/dart-lang/sse
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/sse
 
 environment:
   sdk: ^3.3.0