Legacy Contacts: add `GetExportJobsAsync`

[Jericho]

This new feature will be rolled out by SendGrid between May 12 and June 30, 2025 according to email received on March 10 2025.

This new feature is documented here: https://www.twilio.com/docs/sendgrid/ui/sending-email/update-to-legacy-api-2025q1#added-export-resources

[Jericho]

The page where this new feature was documented (which I linked in my original comment) no longer exist.