Add copilot-requests permission, gated by feature flag (#335)

* Add copilot-requests permission gated by feature flag

This add a new 'copilot-requests' permission to the workflow schema,
gated behind the 'allowCopilotRequestsPermission' experimental
feature flag.

When the flag is disabled (default), `copilot-requests` is filtered
out of autocomplete suggestions. When enabled, it appears
alongside other permissions like actions, contents, pull-requests,
etc.

* Update workflow-parser/src/workflow-v1.0.json

* Add additional unit test coverage

* Fix formatting

workflow-parser/src/workflow-v1.0.json

@@ -1602,6 +1602,10 @@
             "type": "permission-level-any",
             "description": "Repository contents, commits, branches, downloads, releases, and merges."
           },
+          "copilot-requests": {
+            "type": "permission-level-write-or-no-access",
+            "description": "GitHub Copilot requests."
+          },
           "deployments": {
             "type": "permission-level-any",
             "description": "Deployments and deployment statuses."