Add importprivkeys RPC

The development of a Python-based tool named Core-Wallet-Migration-Tools available on GitHub aims to address these challenges by facilitating the migration of private keys into Bitcoin Core descriptor wallets. This tool supports both legacy and Bech32/SegWit private keys, showcasing a tangible step towards simplifying user interactions with Bitcoin Core wallets. However, the discourse underlines a more profound need for an integrated solution within Bitcoin Core to streamline this process further. A proposed solution to this issue is the introduction of an 'importprivkeys' RPC call designed specifically for descriptor wallets. This new command would allow the direct importation of Wallet Import Format (WIF) keys into descriptor wallets, distinguishing it from the 'importprivkey' call used for legacy wallets. The incorporation of this functionality aims to significantly improve the user experience by simplifying the management of private keys within these modern wallet structures. Further details and the technical rationale behind this proposal are elaborated in a document made accessible through Gist, emphasizing the initiative's potential to contribute to the Bitcoin development community's goals of enhancing accessibility and efficiency in digital asset management. Feedback on the proposal has highlighted areas for refinement, such as optimizing the return scheme used by importdescriptors to potentially simplify implementation efforts. The suggestion includes unifying redundant or competing returns, which could streamline the process by either complementing or acting as a proxy to the 'importdescriptors' routine. Additionally, the conversation has brought to light the absence of a checksum induction flag within the importdescriptors functionality, pointing out an opportunity to enhance this command's utility and efficiency. Introducing an 'auto_checksum' boolean could reduce dependency on the proposed 'importprivkeys' command, suggesting a path towards a more robust and user-friendly system for importing descriptors and private keys. These insights reflect a proactive stance towards addressing technical limitations, aiming to foster a more accessible and efficient environment for managing Bitcoin Core descriptor wallets.