Add cross-repo issue analysis agentic workflow (#670)

* Add cross-repo issue analysis agentic workflow

Adds an agentic workflow that analyzes issues filed in copilot-sdk to
determine if the root cause is in copilot-agent-runtime. When a runtime
fix is needed, it automatically creates a linked issue and draft PR in
the runtime repo.

Triggers on new issues and manual workflow_dispatch. Requires a
CROSS_REPO_PAT secret with access to both repos.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Rename secret to RUNTIME_TRIAGE_TOKEN

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: patniko

.github/aw/actions-lock.json

@@ -20,6 +20,11 @@
       "version": "v7.0.0",
       "sha": "bbbca2ddaa5d8feaa63e36b76fdaad77386f024f"
     },
+    "github/gh-aw/actions/setup@v0.50.5": {
+      "repo": "github/gh-aw/actions/setup",
+      "version": "v0.50.5",
+      "sha": "a7d371cc7e68f270ded0592942424548e05bf1c2"
+    },
     "github/gh-aw/actions/setup@v0.52.1": {
       "repo": "github/gh-aw/actions/setup",
       "version": "v0.52.1",