결과 요청시 항목 필터링 기능 추가 (ex: 19대 의안만 반환)

[e9t]

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[e9t]

statements의 date parameter 외에도, bills 의 assembly_id parameter 등에도 filtering 기능이 필요. Suggested by @hunkim at https://github.com/teampopong/popong-api/issues/9