* docs: add Apache Iceberg FDW docs * docs: add DuckDB FDW docs * fix(tests): fix docs tests erroring in CI GitHub Auth was enabled in our supabase config.toml, which causes the supabase startup to try finding GITHUB_CLIENT_ID and GITHUB_CLIENT_SECRET in env. We don't actually need these for tests, so we can just mock them. --------- Co-authored-by: Charis Lam <26616127+charislam@users.noreply.github.com>