Put zed: open account settings action behind a feature flag (#17014)

This PR puts the `zed: open account settings` action behind the
`zed-pro` feature flag, as it isn't supposed to be visible to users yet.

Closes https://github.com/zed-industries/zed/issues/17010.

Release Notes:

- N/A

Cargo.lock

@@ -14110,6 +14110,7 @@ dependencies = [
  "collab_ui",
  "collections",
  "command_palette",
+ "command_palette_hooks",
  "copilot",
  "db",
  "dev_server_projects",
@@ -14118,6 +14119,7 @@ dependencies = [
  "env_logger",
  "extension",
  "extensions_ui",
+ "feature_flags",
  "feedback",
  "file_finder",
  "file_icons",