Document `AllowPublicKeyRetrieval` in migrating doc

[bgrainger]

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Starting in 8.0.10, Connector/NET allows AllowPublicKeyRetrieval to be set in the connection string: https://dev.mysql.com/doc/connector-net/en/connector-net-8-0-connection-options.html

Need to update https://github.com/mysql-net/MySqlConnector/blob/e5cc8114730eaaa2c45921db688da3e17152c8ae/docs/content/tutorials/migrating-from-connector-net.md?plain=1#L51