On ESP IDF 5.5 the get_current_time tool returns ESP_ERR_NOT_FOUND because
there is no "Date" header. This is because esp_http_client_get_header
only reads request headers. Response headers are only available via the
HTTP_EVENT_ON_HEADER event callback. They're dispatched and freed as they're
parsed.
Register an event handler that captures the "Date" header during HTTP response
parsing. The date string from this header is available as part of user context
after the HTTP request is finished.
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