feat: filter users by github user id in the users list CLI command (#17029)

Add the `--github-user-id` option to `coder users list`, which makes the
command only return users with a matching GitHub user id. This will
enable https://github.com/coder/start-workspace-action to find a Coder
user that corresponds to a GitHub user requesting to start a workspace.

cli/testdata/coder_users_list_--help.golden

@@ -9,6 +9,9 @@ OPTIONS:
   -c, --column [id|username|email|created at|updated at|status] (default: username,email,created at,status)
           Columns to display in table output.
 
+      --github-user-id int
+          Filter users by their GitHub user ID.
+
   -o, --output table|json (default: table)
           Output format.