Add support for XLS-0052-NFTokenMintOffer

Added Support for [NFTokenMintOffer](https://github.com/XRPLF/XRPL-Standards/blob/master/XLS-0052-NFTokenMintOffer/README.md).

@tequdev As an effort to keep both xrpl.js and xrpl-py client libraries in sync, would you like to add support for NFTokenMintOffer in xrpl-py?

Reference xrpl.js PR: https://github.com/XRPLF/xrpl.js/pull/2875