feat: add POST method and body support to multi_format_api_handler

[gabrielbressan-tfy]

Summary

• Adds method connection arg (STR, GET or POST, default GET) — fully backward-compatible
• Adds body connection arg (DICT) for the default JSON request body sent with POST requests
• Both args are also settable per-query via the WHERE clause (consistent with existing headers pattern)
• POST requests skip the HEAD pre-check (many POST endpoints reject HEAD) and call requests.post(json=body)
• Body is shallow-merged: connection-level body provides defaults, query-level keys override them

Usage

-- POST at query level
SELECT * FROM handler.data
WHERE url = 'https://api.example.com/search'
  AND method = 'POST'
  AND body = '{"query": "test", "limit": 10}';

-- POST at connection level
CREATE DATABASE my_api WITH ENGINE = 'multi_format_api', PARAMETERS = {
  "url": "https://api.example.com/search",
  "method": "POST",
  "body": {"api_key": "abc", "query": "default"}
};
SELECT * FROM my_api.data;