[FEATURE] Add RDAP flag in RequestParameters

[yfidouh]

Overview

The WHOIS API already supports an rdap flag, but there is currently no way to set this flag in the RequestParameters class within the Python client library.

Proposal

Add an rdap parameter to the RequestParameters class so that users can set rdap=1 (with the default rdap=0, consistent with the Whois API documentation) when building their request. This would help the Python client fully support the existing API functionality.

Example Usage

# Current usage (no RDAP support):
params = RequestParameters(ignore_raw_texts=1, da=2)  # etc.
# params.rdap = ?

# Proposed usage:
params = RequestParameters(rdap=1, **kwargs)